Feather keratin hydrolysates obtained from microbial keratinases: effect on hair fiber

Nutritional and technological potential of chicken feathers for the food industry

1. The production of chicken meat has resulted in high volumes of byproducts, such as feathers, bones, skin, viscera, and feet. The structure of feathers is one of the most complex among vertebrates, with a central axis and lateral filamentary structures, providing rigidity, lightness, and flexibility. Chicken feathers are composed of proteins, lipids, and water, with the highest protein content, especially keratin, which is responsible for the material's rigidity.2. Industries still make little use of feathers, which are generally intended for the production of flour or organic fertilisers. These are low added value products, and discarded feathers can harm the environment.3. Keratin extraction techniques and resulting protein hydrolysates have been studied in chicken feathers. Acid, alkaline or enzymatic hydrolysis is the most commonly used method for obtaining molecules with functional properties such as antioxidant, antimicrobial, antihypertensive and antidiabetic activity.4. The development of keratin-based biodegradable films represents an area of interest for reducing the economic and environmental impacts caused by inappropriate disposal of feathers.

Harnessing the potential of microbial keratinases for bioconversion of keratin waste

The increasing global consumption of poultry meat has led to the generation of a vast quantity of feather keratin waste daily, posing significant environmental challenges due to improper disposal methods. A growing focus is on utilizing keratinous polymeric waste, amounting to millions of tons annually. Keratins are biochemically rigid, fibrous, recalcitrant, physiologically insoluble, and resistant to most common proteolytic enzymes. Microbial biodegradation of feather keratin provides a viable solution for augmenting feather waste's nutritional value while mitigating environmental contamination. This approach offers an alternative to traditional physical and chemical treatments. This review focuses on the recent findings and work trends in the field of keratin degradation by microorganisms (bacteria, actinomycetes, and fungi) via keratinolytic and proteolytic enzymes, as well as the limitations and challenges encountered due to the low thermal stability of keratinase, and degradation in the complex environmental conditions. Therefore, recent biotechnological interventions such as designing novel keratinase with high keratinolytic activity, thermostability, and binding affinity have been elaborated here. Enhancing protein structural rigidity through critical engineering approaches, such as rational design, has shown promise in improving the thermal stability of proteins. Concurrently, metagenomic annotation offers insights into the genetic foundations of keratin breakdown, primarily predicting metabolic potential and identifying probable keratinases. This may extend the understanding of microbial keratinolytic mechanisms in a complex community, recognizing the significance of synergistic interactions, which could be further utilized in optimizing industrial keratin degradation processes.

Effects of various substances on the binding of keratin monomers to S. maltophilia DHHJ cells for the induction of keratinase production

Biodegradation effectiveness of S. maltophilia DHHJ is determined by its ability to attach to the hydrolyzed feather keratin monomers. This binding capacity can be influenced by many components in the culture medium. Keratin monomers from feathers or those produced by gene overexpression can induce keratinase production in S. maltophilia DHHJ, and several proteases lack the ability to degrade keratin fragments and cysteines. In this study, we co-incubated FITC-labelled keratin monomers with S. maltophilia DHHJ cells in the presence of BSA, DNA, ATP, and several metal ions, and measured fluorescence values and keratinase activity. BSA was found to compete with keratins for cell binding sites, resulting in less keratinase production. DNA did not interfere with cellular binding to keratins revealing unchanged keratinase level. ATP, along with metal ions, enhanced the cellular binding capacity to keratins and increased the production of keratinase by S. maltophilia DHHJ. Fragments of keratin monomers degraded by proteases reduced the ability of cells to bind to keratin and affected enzyme production. Cysteine, a characteristic amino acid of feather keratin, did not have an effect on cellular binding to keratin monomer or on keratinase production. This study will facilitate the tweaking of catalytic parameters to improve feather biodegradation by S. maltophilia DHHJ.

Degradation of tannery hide raw trimming hairs using keratinolytic bacteria isolated from tannery effluent-contaminated soil

The disposal of keratinous wastes produced by several leather industries is evolving into a global problem. Around 1 billion tonnes of keratin waste are released into the environment each year. In the breakdown of tannery waste, certain enzymes, such as keratinases produced from microorganisms, might be a better substitute for synthetic enzymes. Keratinase enzymes are able to hydrolyze gelatin, casein, bovine serum albumin and insoluble protein present in wool, feather. Therefore, in this study, bacterial strains from tannery effluent-contaminated soil and bovine tannery hide were isolated and assessed for their ability to produce the keratinolytic enzyme. Among the six isolates, the strain NS1P showed the highest keratinase activity (298 U/ml) and was identified as Comamonas testosterone through biochemical and molecular characterization. Several bioprocess parameters such as pH, temperature, inoculum size, carbon sources, and nitrogen sources were optimized in order to maximize crude enzyme production. The optimized media were used for inoculum preparation and subsequent biodegradation of hide hairs. The degradation efficacy of the keratinase enzyme produced by Comamonas testosterone was examined by degrading bovine tannery hide hairs, and it was found to be 73.6% after 30 days. The morphology of the deteriorated hair was examined using a field emission scanning electron microscope (FE-SEM), which revealed significant degradation. Thus, our research work has led to the conclusion that Comamonas testosterone may be a promising keratinolytic strain for the biodegradation of tannery bovine hide hair waste and the industrial production of keratinases.

Enzymatic Crosslinking of Amino Acids Improves the Repair Effect of Keratin on Hair Fibre

Although keratin can effectively repair hair fibres and enhance their moisture content and flexibility, it has a relatively low affinity for hair. In this study, the effects of transglutaminase (TGase)-commonly used to catalyse crosslinking of proteins or amino acids-in crosslinking serine and hydrolysed wool keratin to repair damaged hair and protect healthy hair were studied. Treatment with a repair solution containing hydrolysed wool keratin, serine, and TGase improved the physical and chemical properties of damaged hair samples. The alkali solubility of damaged hair samples decreased by 50.53%, fracture stress increased from 1.031 to 1.806 N, and fracture strain increased from 9.51 to 19.88 mm. Fourier transform infrared spectroscopy and X-ray analysis showed that amide bonds increased in damaged hair samples treated with the repair solution and hair crystallinity increased. Differential scanning calorimetry showed that the repair solution improved the thermal stability of damaged hair. After five cycles of washing, the effects of the repair solution were still apparent in damaged hair samples. The enzymatic solution had stronger repair effects than general hair care products and reduced water loss rates in damaged hair samples; repaired hair samples were also softer and brighter. The repair solution was effective in protecting healthy hair samples against chemical damage. The materials used to prepare the repair solution are all bio-based, and treatment with this product is safer and longer lasting.

Optimization of Keratin Hydrolysate Extraction from Tannery Sheep Hair Waste

Tannery hair wastes are becoming a challenge for tanners regarding environmental pollution control and human health. In this study, an experiment had been designed to hydrolyse sheep hair in an alkaline medium, and the operational condition for the alkaline extraction of KH has been modeled and optimized. The structure, morphology, functional groups, particle size, and molecular mass of the KH extracts were evaluated experimentally by scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy (FTIR), particle size analysis, and SDS-PAGE analysis, respectively. FTIR analysis of the extract confirmed the presence of carboxylic, amide, and aldehyde functional groups and alkyl side chains of amino acids. The molecular weight of the extracted keratin ranges between 3–15 kDa, and X-ray diffraction (XRD) analysis showed an amorphous form of structure with two peaks at 2 theta of 9.36° and 21.16° due to $\alpha$ -helix and $\beta$ - sheet structure in keratin. Response surface methodology (RSM) coupled with BOX-Behnken design was applied as a statistical tool to investigate the effect of extraction time, the concentration of the hydrolysing agent, and temperature on the response variable (yield of keratin protein). The concentration of the hydrolysing agent was found to be the most significant factor affecting the speed of extraction, but its gradual increase tends to affect the protein content of the extract. Optimum parameters of 0.5 N, 80°C, and 3.5 hr were obtained for the concentration of NaOH, temperature, and extraction time, respectively, with a maximum average protein yield of 91.5% and a percentage total nitrogen content of 14.6% using the Kjeldahl method and 86.57% using the biuret test method.

Impact of Acid ("Progressive Brush") and Alkaline Straightening on the Hair Fiber: Differential Effects on the Cuticle and Cortex Properties

Background

Glyoxylic acid has emerged as a safe alternative to formol (formaldehyde) use as a hair straightener/relaxer. However, the possible damage to the hair fiber after its application is low known and/or published in the literature.

Aims

This work aims to characterize hair locks treated with glyoxylic acid compared to traditional alkaline straighteners such as sodium and guanidine hydroxide and ammonium thioglycolate.

Materials and Methods

The morphology of the hair cuticles was observed by scanning electron microscopy. Protein loss was assessed by the Lowry method modified by Peterson and as mechanical properties that were expressed in terms of tensile strength.

Results

All products (sodium and guanidine hydroxides and ammonium thioglycolate) caused protein loss of about 2.5 μg/g, except glyoxylic acid that caused the worst damage (3.5 μg/g), in relation to the untreated (virgin) hair (1.12 μg/g), indicating that the chemical treatments can cause hair damage in both cuticles and cortex. The force to break the fibers treated with traditional straighteners based on sodium hydroxide, guanidine hydroxide, and ammonium thioglycolate was statistically the same.

Conclusion

The treatment with glyoxylic acid showed rupture tensile statistically equivalent to the alkaline straighteners. The mechanism of action of glyoxylic acid does not appear to be based on breaking and rearrangement of disulfide bridges, but altered them, that influenced the hair strength. However, it is also essential to consider other factors relevant: technical application technique, reaction time, and interval of reapplication of the product, as this can change the pattern of the results obtained.

Feather-Degrading Bacillus cereus HD1: Genomic Analysis and Its Optimization for Keratinase Production and Feather Degradation

Keratinase is an important enzyme that is used to degrade feather wastes produced by poultry industries and slaughterhouses that accumulate rapidly over time. The search for keratinase-producing microorganisms is important to potentially substitute physicochemical treatments of feather waste. In this study, the genome of Bacillus cereus HD1 and its keratinolytic prowess was investigated. The whole-genome shotgun size is 5,668,864 bp consisting of 6083 genes, 69 tRNAs, and 10 rRNAs. The genomic analyses revealed 15 potential keratinase genes and other enzymes that might assist keratin degradation, such as disulfide reductase and cysteine dioxygenase. The optimal conditions for feather degradation and keratinase production by B. cereus HD1 such as incubation time, pH, temperature, yeast extract, and glycerol concentrations were determined to be 5 days, pH 8, 37 °C, 0.05% (w/v), and 0.1% (v/v), respectively. Under optimized conditions, B. cereus HD1 exhibited feather degradation of 65%, with bacterial growth and maximum keratinase activity of 1.3 × 10¹¹ CFU/mL and 41 U/mL, respectively, after 5 days of incubation in a feather basal medium. The findings obtained from this study may facilitate further research into utilizing B. cereus HD1 as a prominent keratinolytic enzymes production host and warrant potential biotechnological applications.

Enhanced keratinase production by Bacillus subtilis amr using experimental optimization tools to obtain feather protein lysate for industrial applications

The poultry industry produces millions of tons of feathers waste that can be transformed into valuable products through bioprocess. The study describes the enhanced keratinase and feather hydrolysate production by Bacillus subtilis AMR. The metabolism of each microorganism is unique, so optimization tools are essential to determine the best fermentation parameters to obtain the best process performance. The evaluation of different propagation media indicated the constitutive production of two keratinases of approximately 80 kDa. The combination of Mn²⁺, Ca²⁺, and Mg²⁺ at 0.5 mM improved the keratinolytic activity and feather degradation 1.5-fold, while Cu²⁺ inhibited the enzymatic activity completely. Replace yeast extract for sucrose increased the feather hydrolysate production three times. The best feather concentration for hydrolysate production was 1.5% with an inoculum of 10⁸ CFU/mL and incubation at 30 °C. None of the inorganic additional nitrogen sources tested increased hydrolysate production, although (NH₄)₂SO₄ and KNO₃ improved enzymatic activity. The optimization process improved keratinolytic activity from 205.4 to 418.7 U/mL, the protein concentration reached 10.1 mg/mL from an initial concentration of 3.9 mg/mL, and the feather degradation improved from 70 to 96%. This study characterized keratinase and feather hydrolysate production conditions offering valuable information for exploring and utilizing AMR keratinolytic strain for feather valorization.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-022-03153-y.

Bioactivity of peptides obtained from poultry by-products: A review

The production and consumption of poultry products (chicken, duck, and turkey) are continually growing throughout the world, leading to the generation of thousands of tons of organic by-products, which may be important sources of bioactive peptides. The bioactive peptides isolated from poultry by-products have biological properties that can be useful in the prevention of different metabolic diseases and hence, their consumption could be beneficial for human health. Such peptides can be used as nutraceuticals, and their inclusion as active components of functional food products is increasingly gaining attention. The aim of this review was to present the investigations of the biological effect of the peptides obtained from different poultry by-products and the possible mechanisms of action underlying these effects.

Performance scanning electron microscopic investigations and elemental analysis of hair of the different animal species for forensic identification

Veterinary forensics have attracted less attention compared with human forensics. Animal hair morphological examination using scanning electron microscopy (SEM) and hair mineral analysis using energy-dispersive X-ray fluorescence (ED-XRF) provide reference databases for animal hair identification used in forensic investigations. This study was performed on four different animal species: large ruminants (buffalo and cattle), small ruminants (goat and sheep), carnivores (cat and dog), and equines (donkey and horse). The hair scale pattern, scale margin type, and distance between scales were identified. The hair scale pattern was imbricate in large ruminants, goat, and horse; coronal (crown-like) in carnivores and donkey; and spinous in sheep. The morphometric measurements, including cuticle layer thickness, cuticle scale height, cortex diameter, and hair shaft width were recorded. The highest cuticle thickness was found in horse, and the highest cuticle hair scale was detected in cattle. Moreover, the largest cortex diameter was measured in buffalo, whereas the smallest one was in cat. With regard the content of hair elements, some elements were specific for the hair of certain tested animals, such as bromine in sheep and magnesium and phosphorus in buffalo. In addition, vanadium and titanium were found only in cattle and dog, and the latter element was also detected in sheep. In conclusion, this study provides two techniques for animal hair identification that can be used in forensic investigations.

Effective utilization of tannery hair waste to develop a high-performing re-tanning agent for cleaner leather manufacturing

Accumulation of hair waste is a major burden to the leather industry, causing a negative impact on the industry's sustainable development. The industry is already bogged down by the usage of synthetic re-tanning agents that are not only extremely challenging for biodegradation but also release free-form of formaldehyde in the final leather stage. This research work focuses on developing a formaldehyde-free bio-based re-tanning agent from hair waste. In order to do so, hair waste is subjected to alkali hydrolysis and subsequently graft-copolymerized with methacrylic acid (MAA). These treatments were optimal using 20 % (w/w) sodium hydroxide and thermal activity at 90 °C. This resulted in effective hydrolysis of red sheep hair, which was the ideal candidate in this study. The hydrolysate was subjected to monomer in situ polymerization (using MAA) with potassium per sulfate/sodium meta-bisulphite redox system, leading to the development of keratin hydrolysate-g-methacrylic acid (KH-g-MA) copolymer (this was noted both at a laboratory level and pilot scale). The obtained KH-g-MA copolymer exhibited ideal characteristics such as increased protein content (78.3 ± 1.2), appropriate particle size (1516 nm), suitable pH (5) and required viscosity of 512 cP. The developed KH-g-MA copolymer was then applied as a re-tanning agent in the leather manufacturing process. Significant improvement in leather's mechanical strength characteristics was observed. In addition, the organoleptic properties of leather such as fullness, softness and grain tightness showed much improvement. Scanning electron microscopy (SEM) showed an enhanced surface smoothness and filling of the voids in experimental leather in comparison to the control leather. This recycle and reuse strategy of hair waste not only helps resolve issues with handling of hair solid waste but also results in producing an eco-friendly re-tanning agent in leather manufacturing, thereby paving the way for cyclic economic utilization and cleaner environment.

Valorisation of keratin waste: Controlled pretreatment enhances enzymatic production of antioxidant peptides

Conversion of keratin waste to value-added products not only reduces waste volumes but also creates new revenue streams for the animal production industry. In the present study, combination of alkaline pretreatment of cattle hair with enzymatic hydrolysis was studied to produce keratin hydrolysates with relatively high antioxidant activities. Firstly, the effect of pretreatment conditions at a high solid/liquid mass ratio of 1:2 with different NaOH loadings and temperatures was studied. Increasing NaOH concentration from 1.0% to 2.5% and temperature from room temperature to 110 °C increased hair hydrolysis by keratinase and protein recovery in hydrolysates. Mild pretreatment with 1.5% NaOH at 70 °C for 30 min led to a protein recovery of 30% in the enzymatic hydrolysate. The resulting hydrolysate showed a high antioxidant activity, scavenging 69% of the ABTS radical with a low EC₅₀ of 0.8 mg/mL. Severe pretreatment with 2.5% NaOH at 110 °C for 30 min resulted in a higher protein recovery of 45%, but a lower ABTS radical scavenging activity of 56% and a higher EC₅₀ of 1.3 mg/mL. The reduced antioxidant activity was attributed to the reduced proportion of small peptides (<3 kDa) and the increased extent of amino acid chemical modification. This study demonstrated that controlling alkali pretreatment conditions could lead to the production of enzymatic hydrolysates with higher antioxidant activities for potential value-adding applications. The information generated from this study will aid scale-up and commercialisation of processes with optimised antioxidant peptide production.

Biotechnology of functional proteins and peptides for hair cosmetic formulations

Cosmetics procedures and products combined with environmental insults and daily routines induce irreversible changes in hair. As result of damage, the hair loses some of its properties like strength, elasticity, and smoothness. Recent studies revealed the positive effects of protein-based cosmetics in providing protection to hair. Additionally, these cosmetic products have also shown a great ability to modify hair fibers. We review the effect of protein-based cosmetic formulations on hair properties like color, scent, strength, shape, and volume, highlighting the potential of keratin-based particles and keratin-fusion proteins. In the future, incorporating multifunctional proteins and peptides in the development of alternative hair formulations will result in advanced, sustainable, ecofriendly cosmetic products with a great impact on the cosmetic industry.

Hair Cosmetics for the Hair Loss Patient

Medical professionals that treat patients with alopecia usually lack knowledge about hair cosmetics. Trichologists focus on hair cycling and growth problems and not on the hair shaft integrity. This may lead to abandon of the use of the prescribed treatment, such as topical minoxidil or to inadequate traumatic grooming habits that may jeopardize hair follicle health. Shampoos, hair dyes, and hair-straightening products may alter hair fiber structure, remove lipids, and elude protein. Hair procedures such as hair dying and straightening have side effects and health concerns, especially for pregnant women or sensitive hair and scalp patients. Hair breakage, follicle traction, frizz, contact dermatitis, and mutagenicity are possible side effects of hair cosmetics misuse. The proper use of hair care products may help to increase patients' adherence to alopecia treatments and avoid health problems related to inadequate application of hair cosmetics and procedures.

Microbial proteases: ubiquitous enzymes with innumerable uses

Proteases are ubiquitous enzymes, having significant physiological roles in both synthesis and degradation. The use of microbial proteases in food fermentation is an age-old process, which is today being successfully employed in other industries with the advent of ‘omics’ era and innovations in genetic and protein engineering approaches. Proteases have found application in industries besides food, like leather, textiles, detergent, waste management, agriculture, animal husbandry, cosmetics, and pharmaceutics. With the rising demands and applications, researchers are exploring various approaches to discover, redesign, or artificially synthesize enzymes with better applicability in the industrial processes. These enzymes offer a sustainable and environmentally safer option, besides possessing economic and commercial value. Various bacterial and fungal proteases are already holding a commercially pivotal role in the industry. The current review summarizes the characteristics and types of proteases, microbial source, their current and prospective applications in various industries, and future challenges. Promoting these biocatalysts will prove significant in betterment of the modern world.

One-Pot Process: Microwave-Assisted Keratin Extraction and Direct Electrospinning to Obtain Keratin-Based Bioplastic

Poultry feathers are among the most abundant and polluting keratin-rich waste biomasses. In this work, we developed a one-pot microwave-assisted process for eco-friendly keratin extraction from poultry feathers followed by a direct electrospinning (ES) of the raw extract, without further purification, to obtain keratin-based bioplastics. This microwave-assisted keratin extraction (MAE) was conducted in acetic acid 70% v/v. The effects of extraction time, solvent/feathers ratio, and heating mode (MAE vs. conventional heating) on the extraction yield were investigated. The highest keratin yield (26 ± 1% w/w with respect to initial feathers) was obtained after 5 h of MAE. Waste-derived keratin were blended with gelatin to fabricate keratin-based biodegradable and biocompatible bioplastics via ES, using 3-(Glycidyloxypropyl)trimethoxysilane (GPTMS) as a cross-linking agent. A full characterization of their thermal, mechanical, and barrier properties was performed by differential scanning calorimetry, thermogravimetric analysis, uniaxial tensile tests, and water permeability measurements. Their morphology and protein structure were investigated using scanning electron microscopy and attenuated total reflection-infrared spectroscopy. All these characterizations highlighted that the properties of the keratin-based bioplastics can be modulated by changing keratin and GPTMS concentrations. These bioplastics could be applied in areas such as bio-packaging and filtration/purification membranes.

Closing the Loop with Keratin-Rich Fibrous Materials

One of the agro-industry's side streams that is widely met is the-keratin rich fibrous material that is becoming a waste product without valorization. Its management as a waste is costly, as the incineration of this type of waste constitutes high environmental concern. Considering these facts, the keratin-rich waste can be considered as a treasure for the producers interested in the valorization of such slowly-biodegradable by-products. As keratin is a protein that needs harsh conditions for its degradation, and that in most of the cases its constitutive amino acids are destroyed, we review new extraction methods that are eco-friendly and cost-effective. The chemical and enzymatic extractions of keratin are compared and the optimization of the extraction conditions at the lab scale is considered. In this study, there are also considered the potential applications of the extracted keratin as well as the reuse of the by-products obtained during the extraction processes.

Sustainable enzymatic technologies in waste animal fat and protein management

Waste animal fats and proteins (WAFP) are rich in various animal by-products from food industries. On one hand, increasing production of huge amounts of WAFP brings a great challenge to their appropriate disposal, and raises severe risks to environment and life health. On the other hand, the high fat and protein contents in these animal wastes are valuable resources which can be reutilized in an eco-friendly and renewable way. Sustainable enzymatic technologies are promising methods for WAFP management. This review discussed the application of various enzymes in the conversion of WSFP to value-added biodiesel and bioactivate hydrolysates. New biotechnologies to discover novel enzymes with robust properties were proposed as well. This paper also presented the bio-utilization strategy of animal fat and protein wastes as alternative nutrient media for microorganism growth activities to yield important industrial enzymes cost-effectively.

Ion transfer channel network formed by flower and rod shape crystals of hair hydrolysate in poly(vinyl alcohol) matrix and its application as anion exchange membrane in fuel cells

Ion transfer phenomena occurring in nature are known to be most efficient. Many efforts have been made to mimic such phenomena, especially in the area of energy transfer. Proteins consisting of various amino acids are known to be the fundamental materials behind these phenomena. In the current study, an effort was made to extract proteinaceous material from human hair bio-waste by a green chemical-free thermal hydrolysis process. A simple heat treatment of the human hairs in presence of water led to the formation of a water soluble material, which was called hair hydrolysate (HH), contains 70 wt% proteinaceous material. It was utilized for the fabrication of poly(vinyl alcohol) (PVA) matrix-based anion exchange membrane (AEM). Presence of 27 wt% charged amino acids and 19 wt% polarizable amino acids in the HH provided effective charge transfer sites. 7 wt% arginine present in the HH, having continuous delocalized net positive charge helped the membrane to be stable in highly alkaline conditions, which was confirmed by an indirect analysis of alkaline stability. Formation of rod and flower shaped crystal morphology by the HH in glutaraldehyde crosslinked PVA matrix, created a continuous channel network at higher loadings, which provided a simple path for ion transfer, achieving OH^- conductivity of 7.46 mS/cm at 70 °C. Swelling of the PVA matrix was minimized by annealing of the HH loaded sample, which resulted in reduction of ionic conductivity to 6.16 mS/cm (at 70 °C). At the same time, improvement in the properties like increase in thermal, mechanical and thermo-mechanical stability, reduction in water uptake, %swelling and methanol permeability was observed. The selectivity of the membrane was increased to almost a decimal place. Thus, the HH obtained from simple green thermal hydrolysis of human hair bio-waste is a cheap material, which is found to be suitable as ion conductive material for alkaline fuel cells.

Microbial Keratinase: Next Generation Green Catalyst and Prospective Applications

The search for novel renewable products over synthetics hallmarked this decade and those of the recent past. Most economies that are prospecting on biodiversity for improved bio-economy favor renewable resources over synthetics for the potential opportunity they hold. However, this field is still nascent as the bulk of the available resources are non-renewable based. Microbial metabolites, emphasis on secondary metabolites, are viable alternatives; nonetheless, vast microbial resources remain under-exploited; thus, the need for a continuum in the search for new products or bio-modifying existing products for novel functions through an efficient approach. Environmental distress syndrome has been identified as a factor that influences the emergence of genetic diversity in prokaryotes. Still, the process of how the change comes about is poorly understood. The emergence of new traits may present a high prospect for the industrially viable organism. Microbial enzymes have prominence in the bio-economic space, and proteases account for about sixty percent of all enzyme market. Microbial keratinases are versatile proteases which are continuously gaining momentum in biotechnology owing to their effective bio-conversion of recalcitrant keratin-rich wastes and sustainable implementation of cleaner production. Keratinase-assisted biodegradation of keratinous materials has revitalized the prospects for the utilization of cost-effective agro-industrial wastes, as readily available substrates, for the production of high-value products including amino acids and bioactive peptides. This review presented an overview of keratin structural complexity, the potential mechanism of keratin biodegradation, and the environmental impact of keratinous wastes. Equally, it discussed microbial keratinase; vis-à-vis sources, production, and functional properties with considerable emphasis on the ecological implication of microbial producers and catalytic tendency improvement strategies. Keratinase applications and prospective high-end use, including animal hide processing, detergent formulation, cosmetics, livestock feed, and organic fertilizer production, were also articulated.

Strategies for improved hair binding: Keratin fractions and the impact of cationic substructures

Keratin extracts and hydrolysates from varying sources, their chemical modifications and compositions thereof have shown potential in the restoration of hair properties. Within this study on reactivity of thiol groups and the shielding effect of anionic charges the binding of keratin-associated proteins (KAP) and α-keratins (Ker) extracted from human hair to natural and permed hair fibers was evaluated. Selectively extracted KAP and Ker were preactivated with 6-mercaptonicotinamide in a quantity of 194 ± 21 μmol/g for KAP and 169 ± 27 μmol/g for Ker resulting in 1.9- and 1.4-fold enhanced binding to natural hair, respectively. The amount of accumulated Ker on hair fibers was furthermore increased by 1.7-fold in presence of 25 mM L-arginine. Perming of hair impaired binding characteristics of Ker with negligible effects for preactivation, whereas unmodified and preactivated KAP showed results comparable to natural hair. Strongly enhanced penetrability after perming was reflected by the mean penetration depth for fluorescein of 25 μm compared to 5 μm for natural fibers.

Halloysite/Keratin Nanocomposite for Human Hair Photoprotection Coating

We propose a novel keratin treatment of human hair by its aqueous mixtures with natural halloysite clay nanotubes. The loaded clay nanotubes together with free keratin produce micrometer-thick protective coating on hair. First, colloidal and structural properties of halloysite/keratin dispersions and the nanotube loaded with this protein were investigated. Above the keratin isoelectric point (pH = 4), the protein adsorption into the positive halloysite lumen is favored because of the electrostatic attractions. The ζ-potential magnitude of these core-shell particles increased from -35 (in pristine form) to -43 mV allowing for an enhanced colloidal stability (15 h at pH = 6). This keratin-clay tubule nanocomposite was used for the immersion treatment of hair. Three-dimensional-measuring laser scanning microscopy demonstrated that 50-60% of the hair surface coverage can be achieved with 1 wt % suspension application. Hair samples have been exposed to UV irradiation for times up to 72 h to explore the protection capacity of this coating by monitoring the cysteine oxidation products. The nanocomposites of halloysite and keratin prevent the deterioration of human hair as evident by significant inhibition of cysteic acid. The successful hair structure protection was also visually confirmed by atomic force microscopy and dark-field hyperspectral microscopy. The proposed formulation represents a promising strategy for a sustainable medical coating on the hair, which remediates UV irradiation stress.

A novel thermal hydrolysis process for extraction of keratin from hog hair for commercial applications

We have developed a novel thermal hydrolysis process (THP) to extract and hydrolyze keratin from keratinous animal body wastes without using any chemicals. Our process consists of two heating steps: one is to swell and denature the keratin protein network in the intermediate filaments, while the other is to cleavage the disulfide bonds that connect the tight keratinous fibrils together. Using hog hair as an example, the two-step process achieved a nearly 70% keratin recovery yield, with respect to the original keratin in the hog hair, which is comparable to one of the best recovery yields by conventional chemical processes. The extracted keratin hydrolysate by THP was filtered by the shear wave-induced membrane ultrafiltation for characterization. The molecular weight (MW) analysis using SDS-PAGE and MALDI-TOF mass spectroscopy has demonstrated that our keratin hydrolysis obtained by our two-step THP has a wide range of MW distribution, similar to those already in the hair-care product market. The amino acid composition analysis has shown that our keratin hydrolysate by THP had twice as much essential amino acids as soybean meals on a dry mattter basis. As to the cysteine residue content, we have shown that it can be controlled by adjusting the 2nd heating temperature.

Identification of keratinases from Fervidobacterium islandicum AW-1 using dynamic gene expression profiling

Keratin degradation is of great interest for converting agro‐industrial waste into bioactive peptides and is directly relevant for understanding the pathogenesis of superficial infections caused by dermatophytes. However, the mechanism of this process remains unclear. Here, we obtained the complete genome sequence of a feather‐degrading, extremely thermophilic bacterium, Fervidobacterium islandicum AW‐1 and performed bioinformatics‐based functional annotation. Reverse transcription PCR revealed that 57 putative protease‐encoding genes were differentially expressed in substrate‐dependent manners. Consequently, 16 candidate genes were highly expressed under starvation conditions, when keratin degradation begun. Subsequently, the dynamic expression profiles of these 16 selected genes in response to feathers, as determined via quantitative real‐time PCR, suggested that they included four metalloproteases and two peptidases including an ATP‐dependent serine protease, all of which might act as key players in feather decomposition. Furthermore, in vitro keratinolytic assays supported the notion that recombinant enzymes enhanced the decomposition of feathers in the presence of cell extracts. Therefore, our genome‐based systematic and dynamic expression profiling demonstrated that these identified metalloproteases together with two additional peptidases might be primarily associated with the decomposition of native feathers, suggesting that keratin degradation can be achieved via non‐canonical catalysis of several membrane‐associated metalloproteases in cooperation with cytosolic proteases.

Beyond plucking: Feathers bioprocessing into valuable protein hydrolysates

The livestock production and subsequent processing of meat results in huge quantities of solid waste such as viscera, bones, skin and keratin-rich materials, including feathers, hair, wool, claws and hooves. In particular, the continuous growth of poultry industry generates massive amounts of feathers as major waste material. The conversion of such by-products into materials with increased value has been studied. Hydrothermal, chemical or biological approaches have been investigated to achive effective conversion of highly recalcitrant proteins that are abundant in animal waste, but increasing interest is devoted to the development of biotechnological methods. The processing of feathers and other by-products into protein hydrolysates may have industrial and commercial significance. Therefore, this review comprehensively addresses the postulated applications of hydrolysates obtained from keratinous biomasses. Examples on the utilization of feather hydrolysates as organic soil fertilizers, feed ingredients, cosmetic formulations and biofuel production are described in the literature. Microbial feather hydrolysis can generate bioactive peptides as well. The use of protein-rich waste from meat industry to produce hydrolysates with biological activities constitutes a point of utmost interest for development of functional ingredients with elevated value.

An application of advanced hair-save processes in leather industry as the reason of formation of keratinous waste: few peculiarities of its utilisation

The application of more environmentally friendly hide and skin unhairing technologies in leather processing results in a significant increase in keratin waste. There are currently two most promising hair-saving unhairing methods: enzymatic and hair immunisation. The complete use of hair-saving unhairing methods in the leather industry will lead to the formation of approximately 143 thousand tons of hair/wool waste annually, which will require disposal. The disposal of keratin wastes from the leather industry has not been adequately studied, bearing in mind the possible amount of such wastes that will be produced in the future. Unfortunately, existing studies pay little attention to the method of unhairing, even though the unhairing method has a vast influence on the properties of keratin in the obtained hair/wool wastes. Accordingly, the present research is an attempt to establish how the differently obtained keratin wastes behave following disposal. The obtained results have shown that waste wool is characterised by different behaviour during burial in soil, and the behaviour depends on the method of unhairing. This proposition is valid for waste wool bioresistance as well. It was concluded that the deterioration of any sort of keratinous waste from the leather industry should be investigated thoroughly before disposal by burial in landfills.

Production of feather oligopeptides by a newly isolated bacterium Pseudomonas otitis H11

Oligopeptides usually have high nutritive value and multiple physiological functions. To achieve the highly efficient utilization of feather waste, a feather-degrading bacterium, Pseudomonas otitis, was isolated and used for production of feather oligopeptides. The production potential and characteristics of the produced oligopeptides by H11 were also investigated. The results demonstrated that the optimal initial pH, temperature, fermentation time, and sterilization conditions were 11, 40°C, 24 h, and 121°C for 20 min, respectively. After 24 h of fermentation under the optimal conditions, the feathers were almost completely degraded. Correspondingly, 35.37% oligopeptides (accounting for 69.70% of the total soluble peptides) and varieties of essential amino acids (valine, isoleucine, leucine, phenylalanine, methionine, threonine, and lysine) were obtained. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis indicated that the produced oligopeptides were mainly low molecular weight (below 1600 Da) and rich in branched-chain amino acids. Also, the oligopeptide-enriched hydrolysate displayed good antioxidant activity with 83% 2,2-diphenyl-1-picrylhydrazyl (DPPH•) scavenging ability and 53% superoxide anion (O2•-) scavenging activity. This study demonstrated that the hydrolysate of feathers was abundant in oligopeptide fractions with 5-10amino acid residues and possessed good antioxidant activity. This oligopeptide-enriched hydrolysate could be used as a functional feed supplement and as a source for functional oligopeptide extraction.

Keratinolytic activity of Bacillus subtilis LFB-FIOCRUZ 1266 enhanced by whole-cell mutagenesis

Discarded feathers represent an important residue from the poultry industry and are a rich source of keratin. Bacillus subtilis LFB-FIOCRUZ 1266, previously isolated from industrial poultry wastes, was used in this work and, through random mutation using ethyl methanesulfonate, ten strains were selected based on the size of their degradation halos. The feather degradation was increased to 115% and all selected mutants showed 1.4- to 2.4-fold increase in keratinolytic activity compared to their wild-type counterparts. The protein concentrations in the culture supernatants increased approximately 2.5 times, as a result of feather degradation. The mutants produced more sulfide than the wild-type bacteria that produced 0.45 µg/ml, while mutant D8 produced 1.45 µg/ml. The best pH for enzyme production and feather degradation was pH 8. Zymography showed differences in the intensity and molecular mass of some bands. The peptidase activity of the enzyme blend was predominantly inhibited by PMSF and EDTA, suggesting the presence of serine peptidases. HPTLC analysis evidenced few differences in band intensities of the amino acid profiles produced by the mutant peptidase activities. The mutants showed an increase in keratinolytic and peptidase activities, demonstrating their biotechnological potential to recycle feather and help to reduce the environmental impact.

Identification of Matrix Metalloproteinase-1-Suppressive Peptides in Feather Keratin Hydrolysate

Inhibition of matrix metalloproteinases (MMPs), which degrade collagen and elastin in the dermis of normal skin, is a key strategy for anti-skin aging. In this study, we identified five low-molecular-weight (LMW, <1 kDa) MMP-1-suppressive peptides in feather keratin hydrolysate (FKH) obtained by anaerobic digestion with an extremophilic bacterium. FKH was first subjected to ultrafiltration, followed by size-exclusion chromatography and liquid chromatography/electrospray ionization tandem mass spectrometry analysis. Chemically synthesized peptides identical to the sequences identified suppressed MMP expression in human dermal fibroblasts (HDFs). To investigate the impact of the MMP-1-suppressive peptides on the signaling pathway, we performed antibody array phosphorylation profiling of HDFs. The results suggested that the peptide GGFDL regulates ultraviolet-B-induced MMP-1 expression by inhibiting mitogen-activated protein kinases and nuclear factor κB signaling pathways as well as histone modification. Thus, LMW feather keratin peptides could serve as novel bioactive compounds to protect the skin against intrinsic and extrinsic factors.

Reactive keratin derivatives: A promising strategy for covalent binding to hair

HYPOTHESIS

Restoration of damaged hair structure by replacing lost keratin is still of paramount interest. On account of the fact that native keratin is a highly cross-linked protein with numerous disulfide bonds but just a few nucleophilic thiol groups, binding affinity to hair is comparatively low. Hence, the design of reactive keratin derivatives bearing free sulfhydryl groups that are optionally S-protected and preactivated should enhance permanent binding to hair fibers.

EXPERIMENTS

Keratin was extracted from human Caucasian hair and reduced with NaBH₄ to obtain free sulfhydryl groups (keratin-SH). These thiol groups were S-protected via disulfide linkage to 2-mercaptonicotinic acid (keratin-MNA). Hair fibers were either utilized in their natural form or chemically damaged by bleaching. Amount of keratin derivatives being bound to hair fibers was quantified by fluorescence detection of fluorescein isothiocyanate labeled keratins.

FINDINGS

Both modifications induced higher affinity of keratin to hair fibers, resulting in up to 1.7-fold (keratin-MNA) improved binding to natural hair and up to 3.6-fold (keratin-MNA) improved binding to bleached hair. Confocal laser microscopy confirmed the accumulation of keratin derivatives in distinct regions of the cuticle layer. Thiol functionalization seems therefore to be a promising strategy for efficient durable binding of keratin to hair.

Low-molecular weight keratins with anti-skin aging activity produced by anaerobic digestion of poultry feathers with Fervidobacterium islandicum AW-1

Bioactive peptides contribute to various cellular processes including improved skin physiology. Hence, bioactive keratins have attracted considerable attention as active cosmetic ingredients for skin health. Here, we obtained low molecular weight (LMW) keratins from native chicken feathers by anaerobic digestion with an extremely thermophilic bacterium Fervidobacterium islandicum AW-1, followed by stepwise fractionation through ultrafiltration. To assess the effects of the feather keratins on skin health, we performed in vitro and ex vivo assays to investigate their inhibitory effects on matrix metalloproteinases (MMPs). As results, LMW feather keratins marginally inhibited collagenase, elastase, and radical scavenging activities. On the other hand, LMW feather keratins significantly suppressed the expression of ultraviolet B (UVB)-induced MMP-1 and MMP-13 in human dermal fibroblasts. Furthermore, phospho-kinase antibody array revealed that LMW feather keratins suppressed UVB-induced phosphorylation of Akts, c-Jun N-terminal kinases 1, p38 beta, and RSK2, but not ERKs in human dermal fibroblast. Overall, these results suggest that LMW feather keratins are potential candidates as cosmeceutical peptides for anti-skin aging.

Effect of a peptide in cosmetic formulations for hair volume control

OBJECTIVE

The capacity of hair to absorb water causes changes in its physical and cosmetic properties under different environmental conditions. Hence, the control of hair volume in variable relative humidity settings is an important topic in cosmetics. The behaviour of two types of hair, Caucasian and Asian, was studied regarding their volume change in different relative humidity conditions. The ability of a peptide as a hair volume treatment was evaluated in two climate control formulations.

METHODS

Tresses of the two types of hair were tested in two relative humidity (RH) conditions: (A) variable relative humidity (2 h 40% RH, followed by 2 h 90% RH and 2 h of 40% RH), and (B) continuous high relative humidity (90% RH for 6 h). Changes in the hair tress volume were assessed throughout time. Hair treated with two climate control formulations, with and without a peptide (KP peptide), were tested under the two relative humidity conditions.

RESULTS

Caucasian hair had a higher change in volume compared to the Asian hair in variable and high relative humidity conditions. The hair volume increase when subject to high air humidity, and it was lower with the incorporation of a peptide into climate control formulations.

CONCLUSION

Caucasian hair showed higher volume than Asian hair when submitted to both relative humidity conditions. The incorporation of the peptide into the climate control formulations, a base (mostly composed of water ≈ 94%) and an ethanolic, was found to reduce the volume of Caucasian hair tresses. The presence of the peptide improved the hair volume change more than 60% in high relative humidity conditions.

Protein-protein cross-linking and human health: the challenge of elucidating with mass spectrometry

INTRODUCTION

In several biomedical research fields, the cross-linking of peptides and proteins has an important impact on health and wellbeing. It is therefore of crucial importance to study this class of post-translational modifications in detail. The huge potential of mass spectrometric technologies in the mapping of these protein-protein cross-links is however overshadowed by the challenges that the field has to overcome. Areas covered: In this review, we summarize the different pitfalls and challenges that the protein-protein cross-linking field is confronted with when using mass spectrometry approaches. We additionally focus on native disulfide bridges as an example and provide some examples of cross-links that are important in the biomedical field. Expert commentary: The current flow of methodological improvements, mainly from the chemical cross-linking field, has delivered a significant contribution to deciphering native and insult-induced cross-links. Although an automated data analysis of proteome-wide peptide cross-linking is currently only possible in chemical cross-linking experiments, the field is well on the way towards a more automated analysis of native and insult-induced cross-links in raw mass spectrometry data that will boost its potential in biomedical applications.

Development of a keratinase activity assay using recombinant chicken feather keratin substrates

Poultry feathers consist mainly of the protein keratin, which is rich in β-pleated sheets and consequently resistant to proteolysis. Although many keratinases have been identified, the reasons for their substrate specificity towards β-keratin remain unclear due to difficulties in preparing a soluble feather keratin substrate for use in activity assays. In the present study, we overexpressed Gallus gallus chromosomes 2 and 27 β-keratin-encoding genes in Escherichia coli, purified denatured recombinant proteins by Ni²⁺ affinity chromatography, and refolded by stepwise dialysis to yield soluble keratins. To assess the keratinolytic activity, we compared the proteolytic activity of crude extracts from the feather- degrading bacterium Fervidobacterium islandicum AW-1 with proteinase K, trypsin, and papain using purified recombinant keratin and casein as substrates. All tested proteases showed strong proteolytic activities for casein, whereas only F. islandicum AW-1 crude extracts and proteinase K exhibited pronounced keratinolytic activity for the recombinant keratin. Moreover, LC-MS/MS analysis of keratin hydrolysates allowed us to predict the P1 sites of keratinolytic enzymes in the F. islandicum AW-1 extracts, thereby qualifying and quantifying the extent of keratinolysis. The soluble keratin-based assay has clear therapeutic and industrial potential for the development of a high-throughput screening system for proteases hydrolyzing disease-related protein aggregates, as well as mechanically resilient keratin-based polymers.

Changing the shape of hair with keratin peptides

Here we propose a solution which will replace harsh reducing agents at alkaline pH by peptide formulations acting at neutral pH to change hair shape through the re-conformation of disulphide bonds.

Production of Thermostable Organic Solvent Tolerant Keratinolytic Protease from Thermoactinomyces sp. RM4: IAA Production and Plant Growth Promotion

There are several reports about the optimization of protease production, but only few have optimized the production of organic solvent tolerant keratinolytic proteases that show remarkable exploitation in the development of the non-polluting processes in biotechnological industries. The present study was carried with aim to optimize the production of a thermostable organic solvent tolerant keratinolytic protease Thermoactinomyces sp. RM4 utilizing chicken feathers. Thermoactinomyces sp. RM4 isolated from the soil sample collected from a rice mill wasteyard site near Kashipur, Uttrakhand was identified on the basis of 16S rDNA analysis. The production of organic solvent tolerant keratinolytic protease enzyme by Thermoactinomyces sp. RM4 was optimized by varying physical culture conditions such as pH (10.0), temperature (60°C), inoculum percentage (2%), feather concentration (2%) and agitation rate (2 g) for feather degradation. The result showed that Thermoactinomyces sp. RM4 potentially produces extra-cellular thermostable organic solvent tolerant keratinolytic protease in the culture medium. Further, the feather hydrolysate from keratinase production media showed plant growth promoting activity by producing indole-3-acetic acid itself. The present findings suggest that keratinolytic protease from Thermoactinomyces sp. RM4 offers enormous industrial applications due to its organic solvent tolerant property in peptide synthesis, practical role in feather degradation and potential function in plant growth promoting activity, which might be a superior candidate to keep ecosystem healthy and functional.

Purification and partial characterization of serine-metallokeratinase from a newly isolated Bacillus pumilus NRC21

A serine metallokeratinase enzyme (30 kDa) produced by a newly isolated Bacillus strain (Bacillus pumilus NRC21) cultivated under optimized conditions in medium containing chicken feather meal was purified and characterized in a set of biochemical assays. The purification was carried out using two successive chromatographic steps; cation exchange chromatography on CM-cellulose and gel filtration on sephadex G-100 columns. The purified enzyme showed a specific activity of 2000 units/mg protein against 170 units/mg protein for crude extract with 12 fold purification. The enzymatic activity of the keratinase stimulated by (Na(+), K(+), Mg(2+)), Hg(+2) had no effect, and inhibited by entire tested cations, serine and metalloproteinase inhibitors, therefore it can be considered as a serine metalloenzyme. The optimum pH and temperature for the purified enzyme were (7.5, 8.5) and (50, 45 °C) when using keratin azure and azocasein as substrates, respectively. The purified enzyme was highly stable at broad pH and temperature ranged (5-10) and (20-60 °C), respectively and its thermoactivity and thermostability were enhanced in the presence of 5 mM Mg(+2). These results suggest that the purified keratinase may be used in several industrial applications.

Improved radiocarbon analyses of modern human hair to determine the year-of-death by cross-flow nanofiltered amino acids: common contaminants, implications for isotopic analysis, and recommendations

RATIONALE

In forensic investigation, radiocarbon ((14)C) measurements of human tissues (i.e., nails and hair) can help determine the year-of-death. However, the frequent use of cosmetics can bias hair (14)C results as well as stable isotope values. Evidence shows that hair exogenous impurities percolate beyond the cuticle layer, and therefore conventional pretreatments are ineffective in removing them.

METHODS

We conducted isotopic analysis ((14)C, δ(13)C, δ(15)N and C/N) of conventionally treated and cross-flow nanofiltered amino acid (CFNAA)-treated samples (scalp- and body-hair) from a single female subject using fingernails as a reference. The subject studied frequently applies a permanent dark-brown dye kit to her scalp-hair and uses other care products for daily cleansing. We also performed pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) analyses of CFNAA-treated scalp-hair to identify contaminant remnants that could possibly interfere with isotopic analyses.

RESULTS

The conventionally treated scalp- and body-hair showed (14)C offsets of ~21‰ and ~9‰, respectively. These offsets confirm the contamination by petrochemicals in modern human hair. A single CFNAA extraction reduced those offsets by ~34%. No significant improvement was observed when sequential extractions were performed, as it appears that the procedure introduced some foreign contaminants. A chromatogram of the CFNAA scalp-hair pyrolysis products showed the presence of petroleum and plant/animal compound residues, which can bias isotopic analyses.

CONCLUSIONS

We have demonstrated that CFNAA extractions can partially remove cosmetic contaminants embedded in human hair. We conclude that fingernails are still the best source of keratin protein for year-of-death determinations and isotopic analysis, with body-hair and/or scalp-hair coupled with CFNAA extraction a close second.

Keratinous waste decomposition and peptide production by keratinase from Geobacillus stearothermophilus AD-11

A keratinolytic proteinase was cloned from thermophilic bacterium Geobacillus stearothermophilus AD-11 and was expressed in Escherichia coli BL21(DE3). Recombinant keratinolytic proteinase (RecGEOker) with an estimated molecular weight of 57 kDa was purified and keratinase activity was measured. RecGEOker showed optimal activity at pH 9 and 60 °C. Recombinant keratinolytic proteinase showed the highest substrate specificity toward keratin from wool > collagen > sodium caseinate > gelatin > and BSA in descending order. RecGEOker is applicable for efficient keratin waste biodegradation and can replace conventional non-biological hydrolysis processes. High-value small peptides obtained from enzymatic biodegradation by RecGEOker are suitable for industrial application in white and/or green biotechnology for use as major additives in various products.

Hair cosmetics: an overview

Hair cosmetics are an important tool that helps to increase patient's adhesion to alopecia and scalp treatments. This article reviews the formulations and the mode of action of hair cosmetics: Shampoos, conditioners, hair straightening products, hair dyes and henna; regarding their prescription and safetiness. The dermatologist's knowledge of hair care products, their use, and their possible side effects can extend to an understanding of cosmetic resources and help dermatologists to better treat hair and scalp conditions according to the diversity of hair types and ethnicity.