Extraction of watermelon seed proteins with enhanced functional properties using ultrasound

Modification of the physicochemical, functional, biochemical and structural properties of a soursop seed (Annona muricata L.) protein isolate treated with high-intensity ultrasound

The obtained seeds from fruit processing are considered by-products containing proteins that could be utilized as ingredients in food manufacturing. However, in the specific case of soursop seeds, their usage for the preparation of protein isolates is limited. In this investigation a protein isolate from soursop seeds (SSPI) was obtained by alkaline extraction and isoelectric precipitation methods. The SSPI was sonicated at 200, 400 and 600 W during 15 and 30 min and its effect on the physicochemical, functional, biochemical, and structural properties was evaluated. Ultrasound increased (p < 0.05) up to 5 % protein content, 261 % protein solubility, 60.7 % foaming capacity, 30.2 % foaming stability, 86 % emulsifying activity index, 4.1 % emulsifying stability index, 85.4 % in vitro protein digestibility, 423.4 % albumin content, 83 % total sulfhydryl content, 316 % free sulfhydryl content, 236 % α-helix, 46 % β-sheet, and 43 % β-turn of SSPI, in comparison with the control treatment without ultrasound. Furthermore, ultrasound decreased (p < 0.05) up to 50 % particle size, 37 % molecular flexibility, 68 % surface hydrophobicity, 41 % intrinsic florescence spectrum, and 60 % random coil content. Scanning electron microscopy analysis revealed smooth structures of the SSPI with molecular weights ranging from 12 kDa to 65 kDa. The increase of albumins content in the SSPI by ultrasound was highly correlated (r = 0.962; p < 0.01) with the protein solubility. Improving the physicochemical, functional, biochemical and structural properties of SSPI by ultrasound could contribute to its utilization as ingredient in food industry.

Investigating the possibility of increasing the microbial and oxidative stability of silver carp burgers using hydrolyzed protein of watermelon seeds

In this study, watermelon seeds (Citrullus lanatus) protein hydrolyzed (WSPH) was produced using microbial enzymes Alcalase and Protamex. Then, the effect of different concentrations of WSPH (0, 1, 2, and 3%) on the quality of the silver carp (Hypophthalmichthys molitrix) burger during refrigerated storage (4 ± 1 °C) was investigated. According to the results, WSPH by alcalase had significantly higher degree of hydrolysis and antioxidant activity (p < 0.05) and it was used for burger tests. The results showed that, the addition of WSPH was able to reduce the microbial, chemical spoilage and sensory score during 16 days compared to the control, and with increasing the concentration of WSPH, better results were observed (p < 0.05). According to the chemical, microbial and sensory indicators, WSPH at 3% could increase the shelf life of fish burgers up to 8 days compared to the control, and this treatment was within the permissible quality limit until the end of the refrigerated storage.

Graphical abstract

Valorization of protein-rich waste and its application

Energy shortages present significant challenges with the rising population and dramatic urbanization development. The effective utilization of high-value products generated from massive protein-rich waste has emerged as an excellent solution for mitigating the growing energy crisis. However, the traditional disposal and treatment of protein-rich waste, have been proven to be ineffective in resource utilization, which led to high chemical oxygen demand and water eutrophication. To effectively address this issue, hydrolysate and bioconversion products from protein-rich waste have been widely investigated. Herein, we aim to provide an overview of the valorization of protein-rich waste based on a comprehensive analysis of publicly available literature. Firstly, the sources of protein-rich waste with various quantities and qualities are systematically summarized. Then, we scrutinize and analyze the hydrolysis approaches of protein-rich waste and the versatile applications of hydrolyzed products. Moreover, the main factors influencing protein biotransformation and the applications of bioconversion products are covered and extensively discussed. Finally, the potential prospects and future directions for the valorization of protein-rich waste are proposed pertinently.

Ultrasound-assisted alkali removal of proteins from wastewater generated during oil bodies extraction

In this study, an ultrasonic-assisted alkaline method was used to remove proteins from wastewater generated during oil-body extraction, and the effects of different ultrasonic power settings (0, 150, 300, and 450 W) on protein recovery were investigated. The recoveries of the ultrasonically treated samples were higher than those of the samples without ultrasonic treatment, and the protein recoveries increased with increasing power, with a protein recovery of 50.10 % ± 0.19 % when the ultrasonic power was 450 W. Amino acid analysis showed that the amino acids comprising the recovered samples were consistent, regardless of the ultrasonic power used, but significant differences in the contents of amino acids were observed. No significant changes were observed in the protein electrophoretic profile using dodecyl polyacrylamide gel, indicating that sonication did not change the primary structures of the recovered samples. Fourier transform infrared and fluorescence spectroscopy revealed that the molecular structures of the samples changed after sonication, and the fluorescence intensity increased gradually with increasing sonication power. The contents of α-helices and random coils obtained at an ultrasonic power of 450 W decreased to 13.44 % and 14.31 %, respectively, whereas the β-sheet content generally increased. The denaturation temperatures of the proteins were determined using differential scanning calorimetry, and ultrasound treatment reduced the denaturation temperatures of the samples, which was associated with the structural and conformational changes caused by their chemical bonding. The solubility of the recovered protein increased with increasing ultrasound power, and a high solubility was essential in good emulsification. The emulsification of the samples was improved well. In conclusion, ultrasound treatment changed the structure and thus improved the functional properties of the protein.

Ultrasound-Assisted Extraction of Protein from Moringa oleifera Seeds and Its Impact on Techno-Functional Properties

Plant proteins can be an important alternative to animal proteins subject to minor modification to address sustainability issues. The impact of ultrasound application on the yield, techno-functional properties, and molecular characteristics of protein extracted from Moringa oleifera seeds was studied. For this purpose, a central composite design (CCD) was applied to optimize ultrasound-assisted extraction (UAE) parameters such as amplitude (25–75%), solute-to-solvent ratio (1:10–1:30), and pH (9–13) for obtaining the maximum protein yield. At the optimized conditions of 75% amplitude, 1:20 solute-to-solvent ratio, and 11 pH, a protein yield of 39.12% was obtained in the UAE process. Moreover, the best sonication time at optimized conditions was 20 min, which resulted in about 150% more extraction yield in comparison to conventional extraction (CE). The techno-functional properties, for instance, solubility, water (WHC)- and oil-holding capacity (OHC), and emulsifying and foaming properties of the protein obtained from UAE and CE were also compared. The functional properties revealed high solubility, good WHC and OHC, and improved emulsifying properties for protein obtained from UAE. Although protein from UAE provided higher foam formation, foaming stability was significantly lower.

An investigation of correlation between structural and functional properties of Nigella sativa protein isolate

The physicochemical characteristics, amino acid composition, and functional properties of Nigella sativa (NS) seedcake protein extracts were evaluated to establish their potential in nutraceuticals and functional foods. The highest yield (20.2%) of protein isolate (NSPI) from NS seedcake was achieved at an alkali concentration of 0.16 M, a buffer to sample ratio of 1/25 (w/v), extraction time, 15 min, and extraction temperature, 25°C. Amino acid analysis showed that the isolated protein is a good source of amino acids with a significant essential to total amino acid (E/TN) ratio. Further, the protein isolate exhibited maximum solubility at pH 11. The results of the physicochemical analysis clearly indicated that the protein isolate had good water and oil holding capacity, emulsification property, foaming capacity, and foaming stability. The secondary structure of NSPI contained α-helix, β-sheet, and β-turns. In addition, NSPI showed excellent antioxidant, anti-diabetic, and protein digestibility activities. From the experimental data, it could be concluded that NSPI could be an excellent source of proteins for the development of foods with promising functional properties. PRACTICAL APPLICATIONS: Nigella sativa seeds are frequently used as a natural food additive and have been a part of naturopathy for centuries due to their anti-inflammatory, antibacterial, anticancer, antidiabetic, immunomodulatory, and cardioprotective properties. Nigella sativa seedcakes obtained as by-products of the oil extraction process are rich in protein content and can be used as a sustainable source of dietary proteins to cater to a wide range of consumers. Being plant-based, they inherently possess several medicinal properties. Analyzing the physicochemical and functional properties of protein isolated from seedcakes allows us to optimize the protein extraction process while providing a better perspective on its potential in the nutraceuticals and food industries. It can be used as an energy supplement in animal feed as a source of protein to replace soybeans and barley. The antioxidant proteins when added to meat-based products have been known to protect the meat from oxidative stress as well as pathogenic organisms, thus, improving its shelf-life. Nigella sativa protein isolates have several applications in the pharmaceutical industry as well.

Ultrasound-assisted modification of gelation properties of proteins: A review

Protein gels have diverse applications in the food, pharmaceutical, and cosmetic sectors due to their affordability, biodegradability, and edibility. However, the inherent properties of some native proteins have a few drawbacks that have to be tailored to meet the needs of specific functions as the food ingredients. The protein gelation properties mainly depend on the protein molecular structure, primarily the folding and unfolding of secondary structural elements (α-helix and β-sheets) with distinctive functions. In the past, a great amount of work (thermal, chemical, and enzymatic methods) has been carried out to enhance the gelation and functional properties of proteins. Recently, the traditional methods have been replaced with non-thermal physical methods that enhance the properties for better applications. One such approach is the use of ultrasonic technology as a low-cost green technology to modify the molecular orientation attributed to the native chemistry and functionality of that proteins. Ultrasonic technology is important in food systems and can be effectively used as an alternative method to improve the protein gelling characteristics to form high-quality gels. This article is aimed to comprehensively collate some of the vital information published on the mechanism of protein gelation by ultrasonication and review the effects of ultrasound-assisted extraction and treatments on gelation properties of different proteins. The enhanced gelation properties by the ultrasound application open a new stage of technology that enables the proteins for better utilization in the food processing sector.

Valorization of Agro-Industrial Wastes by Ultrasound-Assisted Extraction as a Source of Proteins, Antioxidants and Cutin: A Cascade Approach

The use of agro-industrial wastes to obtain compounds with a high added-value is increasing in the last few years in accordance with the circular economy concept. In this work, a cascade extraction approach was developed based on ultrasound-assisted extraction (UAE) for tomato, watermelon, and apple peel wastes. The protein and antioxidant compounds were obtained during the first extraction step (NaOH 3 wt.%, 98.6 W, 100% amplitude, 6.48 W/cm², 6 min). The watermelon peels (WP) showed higher proteins and total phenolic contents (857 ± 1 mg BSA/g extract and 107.2 ± 0.2 mg GAE/100 g dm, respectively), whereas the highest antioxidant activity was obtained for apple peels (1559 ± 20 µmol TE/100 g dm, 1767 ± 5 µmol TE/100 g dm, and 902 ± 16 µmol TE/100 g dm for ABTS, FRAP and DPPH assays, respectively). The remaining residue obtained from the first extraction was subsequently extracted to obtain cutin (ethanol 40 wt.%, 58 W, 100% amplitude, 2 W/cm², 17 min, 1/80 g/mL, pH 2.5). The morphological studies confirmed the great efficiency of UAE in damaging the vegetal cell walls. WP showed a higher non-hydrolysable cutin content (55 wt.% of the initial cutin). A different monomers’ profile was obtained for the cutin composition by GC-MS, with the cutin from tomato and apple peels being rich in polyhydroxy fatty acids whereas the cutin extracted from WP was mainly based on unsaturated fatty acids. All of the cutin samples showed an initial degradation temperature higher than 200 °C, presenting an excellent thermal stability. The strategy followed in this work has proved to be an effective valorization methodology with a high scaling-up potential for applications in the food, pharmaceutical, nutraceutical, cosmetics and biopolymer sectors.

Influence of high-intensity ultrasound on physicochemical and functional properties of a guamuchil Pithecellobium dulce (Roxb.) seed protein isolate

In this study, the influence of ultrasound on the physicochemical and functional properties of guamuchil seed protein isolate (GSPI) was investigated. The GSPI was prepared by alkaline extraction and isoelectric precipitation method followed by treating with ethanol (95%), from defatted guamuchil seed flour. GSPI suspensions (10%) were sonicated with a probe (20 kHz) at 3 power levels (200 W, 400 W, 600 W) for 15 and 30 min, in addition, to control treatment without ultrasound. Moisture content, water activity, bulk and compact densities and the L*, a* and b* color parameters of the GSPI decreased due to the ultrasound. Glutelin (61.1%) was the main protein fraction in GSPI. Results through Fourier transform infrared and fluorescence spectroscopy showed that ultrasound modified the secondary and tertiary protein structures of GSPI, which increased the surface hydrophobicity, molecular flexibility and in vitro digestibility of GSPI proteins by up to 114.8%, 57.3% and 12.5%, respectively. In addition, maximum reductions of 11.9% in particle size and 55.2% in turbidity of GSPI suspensions, as well as larger and more porous aggregates in GSPI lyophilized powders were observed by ultrasound impact. These structural and physicochemical changes had an improvement of up to 115.5% in solubility, 39.8% in oil absorption capacity, while the increases for emulsifying, foaming, gelling, flow and cohesion properties of GSPI were 87.4%, 74.2%, 40.0%, 44.4%, and 8.9%, respectively. The amelioration of the functional properties of GSPI by ultrasound could represent an alternative for its possible use as a food ingredient in industry.

Ultrasound-assisted processing: Science, technology and challenges for the plant-based protein industry

The present-day consumer is not only conscious of the relationship between food consumption and positive health, but also keen on environmental sustainability. Thus, the demand for plant-based proteins, which are associated with nutrition and environmental sustainability. However, the plant-based protein industry still demands urgent innovation due to the low yield and long extraction time linked with traditional extraction methods. Although ultrasound is an eco-innovative technique, there exist limited data regarding its impact with plant-based protein. In this paper, the scientific principles of ultrasonication with regards to its application in plant-based protein research were reviewed. After comparing the cavitational and shearing impacts of different ultrasonic parameters, the paper further reviewed its effects on extracted protein characteristics and techno-functional properties. Additionally, current technological challenges and future perspectives of ultrasonication for the plant-based protein industry were also discussed. In summary, this review does not only present the novelty and environmental sustainability of ultrasound as a plant-based protein assisted-extraction method, but also highlights on the correlation between protein source, structure and subsequent functional properties which are important crucial factors for maximum application of ultrasound in the growing plant-based protein market.

Identification and characterization of metal-chelating bioenhancer peptide derived from fermented Citrullus lanatus seed milk

In the present investigation, a metal-chelating bioactive peptide was derived from Citrullus lanatus seed milk fermented with Lactococcus lactis. The cationic fermented milk peptide (FMP) thus obtained was purified using the HiTrap-chelating column followed by rpHPLC. The FMP possessed the ability to chelate multiple divalent cations like Cu²⁺ , Ca²⁺ , and Fe²⁺ with 86.81%, 61.04%, and 24.32% of chelation respectively and further it exhibited 78.03% of DPPH free radical scavenging activity. Interaction of FMP with metal ions was assessed by change in the absorption spectra and was analyzed by ultraviolet-visible and fluorescence spectroscopy. The FMP-metal complexes were found stable at simulated gastric conditions. In vitro analysis using intestinal Caco-2 cell lines revealed that there was an increase in metal bioavailability in the presence of the FMP and was least influenced by the addition of a dietary inhibitor, phytic acid. By LC-MS analysis the molecular mass of FMP was found to be 11.6 kD and it contains oxygen-rich and nitrogen-rich amino acids that favor the metal chelation. In our study, we have found that the fermented C. lanatus seed milk can serve as a potential functional food with bioenhancer peptides that increase metal bioavailability and enhance human health. PRACTICAL APPLICATIONS: Chelated metals are preferred over non-chelated ones by most nutritionists for their better absorption rate. Chelation protects the minerals from the digestive process and increases their bioavailability. Fermentation with lactic acid bacteria produces bioactive peptides with metal-chelating and antioxidant ability which provides additional health benefits beyond supplying basic nutrients. Lactococcus lactis fermented milk acts as a probiotic product with bioenhancer peptide that increases mineral bioavailability. Consumption of metals in chelated form can reduce excess intake of metal. Fermented watermelon seed milk can be a promising probiotic drink rich in bioenhancer peptides and can enhance the bioavailability of divalent cations of a high therapeutic index.

Impact of high-intensity ultrasound on the physicochemical and functional properties of a protein isolate from passion fruit (Passiflora edulis) seeds

A protein isolate from passion fruit seeds (PFSPI) obtained by alkaline extraction and isoelectric precipitation was treated with sonication for 15 and 30 min at 40 kHz to evaluate its impact on the physicochemical and functional properties. The PFSPI had a purity of 96.21% protein, with albumins being the main fraction (75.66%). Ultrasound increased the bulk density (ρ) of PFSPI by 13.3% and the formation a more porous structure by a greater separation between particles. Protein solubility of PFSPI in the range of pH 2–12 sonicated for 15 and 30 min, increased on average 5.21 and 9.86%, respectively, in comparison with the control. PFSPI foaming properties were influenced by pH and sonication time, achieving up to 577%, while the minimum gelling concentration was reduced from 4 to 2% at pH 7. Therefore, sonication treatment improved some functional properties of PFSPI for its potential use as a food ingredient.

Rapid extraction of watermelon seed proteins using microwave and its functional properties

Solid food industry waste like watermelon seed is an excellent source of value-added components such as proteins, oil, and carbohydrate. In the present study, protein extraction was carried out using microwave energy from defatted watermelon seeds (DWS), containing 50% of proteins. Microwave-assisted extraction (MAE) was optimized with different parameters, namely, solid to solvent ratio (1:10-1:40), pH (7-10), microwave power (30 W, 50 W, 70 W), extraction time (30 s-8 min) and moisture content or pre-leaching effect. Maximum protein recovery was achieved with 50 W microwave power, solid to solvent ration of 1:30, and pH 10 in 2 minutes of microwave irradiation time. MAE gave higher yield in less time compared to conventional extraction. SDS-PAGE confirmed the molecular weight of watermelon seed proteins (WSP) in the range of 25-250 kDa. A comparative study showed 90% protein recovery with MAE in 2 min with 1:30 (w/v) solid to solvent ratio, whereas ultrasound gave 87% in 9 min with 1:50 (w/v) ratio and batch 72% in 25 min with 1:70 (w/v) ratio. Watermelon seed proteins obtained from MAE method possess excellent functional properties with reference to conventional extraction method indicating its application in food products.