Post-enzymatic hydrolysis heat treatment as an essential unit operation for collagen solubilization from poultry by-products

A portable dry film FTIR instrument for industrial food and bioprocess applications

The main objective of this study was to design, build, and test a compact, multi-well, portable dry film FTIR system for industrial food and bioprocess applications. The system features dry film sampling on a circular rotating disc comprising 31 wells, a design that was chosen to simplify potential automation and robotic sample handling at a later stage. Calibration models for average molecular weight (AMW, 200 samples) and collagen content (68 samples) were developed from the measurements of industrially produced protein hydrolysate samples in a controlled laboratory environment. Similarly, calibration models for the prediction of lactate content in samples from cultivation media (59 samples) were also developed. The portable dry film FTIR system showed reliable model characteristics which were benchmarked with a benchtop FTIR system. Subsequently, the portable dry film FTIR system was deployed in a bioprocessing plant, and protein hydrolysate samples were measured at-line in an industrial environment. This industrial testing involved building a calibration model for predicting AMW using 60 protein hydrolysate samples measured at-line using the portable dry film FTIR system and subsequent model validation using a test set of 26 samples. The industrial calibration in terms of coefficient of determination (R2 = 0.94), root mean square of cross-validation (RMSECV = 194 g mol-1), and root mean square of prediction (RMSEP = 162 g mol-1) demonstrated low prediction errors as compared to benchtop FTIR measurements, with no statistical difference between the calibration models of the two FTIR systems. This is to the authors' knowledge the first study for developing and employing a portable dry film FTIR system in the enzymatic protein hydrolysis industry for successful at-line measurements of protein hydrolysate samples. The study therefore suggests that the portable dry film FTIR instrument has huge potential for in/at-line applications in the food and bioprocessing industries.

The role of biospectroscopy and chemometrics as enabling technologies for upcycling of raw materials from the food industry

It is important to utilize the entire animal in meat and fish production to ensure sustainability. Rest raw materials, such as bones, heads, trimmings, and skin, contain essential nutrients that can be transformed into high-value products. Enzymatic protein hydrolysis (EPH) is a bioprocess that can upcycle these materials to create valuable proteins and fats. This paper focuses on the role of spectroscopy and chemometrics in characterizing the quality of the resulting protein product and understanding how raw material quality and processing affect it. The article presents recent developments in chemical characterisation and process modelling, with a focus on rest raw materials from poultry and salmon production. Even if some of the technology is relatively mature and implemented in many laboratories and industries, there are still open challenges and research questions. The main challenges are related to the transition of technology and insights from laboratory to industrial scale, and the link between peptide composition and critical product quality attributes.

Deepening in the understanding of the role of collagen subunits on the differential molecular arrangement of P. glauca and M. merluccius marine collagens

Decades of extensive efforts on marine collagen extraction and characterization allowed to recognize the unique and excellent characteristics of marine collagen offering advantages over that obtained from terrestrial sources. However, not all marine collagens have the same biochemical characteristics; understanding those at molecular and supramolecular level, is crucial for optimal design of applications. One relevant aspect of collagen characterization is the analysis of its different subunits (α-chains) and their intermolecular cross-links (β- and γ-components), which ultimately determine the specific functions of a particular collagen. Collagens from a teleost and an elasmobranch species were analyzed to understand the influence of their subunit composition and intermolecular crosslinking pattern on their different physicochemical behaviour. For comparative purposes a commercial mammal collagen was included in the study. Although electrophoretic profiles showed the typical composition of type I collagen for hake, blue shark and calf collagen, molar ratios of their α-chains were different indicating a different degree of dimerization of their α2-chains with implications in the presence of a different crosslinking degree pattern. Electrophoresis, amino acid composition, hydrophobicity (RP-HPLC) and molecular weight analysis (GPC-HPLC) results, besides a peptide mapping and an antioxidant activity study of the resultant peptides, would help to understand the role of different subunit collagen composition and different crosslinking pattern in the conformation of a differential quaternary supramolecular structure within different species and its biofunctional implications. The experiments developed would allow to progress in the valorization potential of fish discards and byproducts to explore commercial uses of collagens from marine origin.

FTIR-based prediction of collagen content in hydrolyzed protein samples

Fourier transform infrared spectroscopy (FTIR) is a powerful analytical tool that has been used for protein and peptide characterization for decades. In the present study, the objective was to investigate if FTIR can be used to predict collagen content in hydrolyzed protein samples. All samples were obtained from enzymatic protein hydrolysis (EPH) of poultry by-products providing a span in collagen content from 0.3% to 37.9% (dry weight), and the FTIR analysis was performed using dry film FTIR. Since nonlinear effects were revealed by calibration using standard partial least squares (PLS) regression, Hierarchical Cluster-based PLS (HC-PLS) calibration models were constructed. The HC-PLS model provided a low prediction error when validated using an independent test set (RMSE = 3.3% collagen), while validation using real industrial samples also showed satisfying results (RMSE = 3.2%). The results corresponded well with previously published FTIR-based studies of collagen, and characteristic spectral features for collagen were well identified in the regression models. Covariance between collagen content and other EPH related processing parameters could also be ruled out in the regression models. To the authors' knowledge, this is the first time that collagen content has been systematically studied in solutions of hydrolysed proteins using FTIR. This is also one of few examples where FTIR is successfully used to quantify protein composition. The dry-film FTIR approach presented in the study is expected to be an important tool in the growing industrial segment that is based on sustainable utilization of collagen-rich biomass.

Collagens for surimi gel fortification: Type-dependent effects and the difference between type I and type II

Surimi products have unsatisfactory gel properties. Hence, this study evaluates the effect of collagen-adding on surimi gel properties and provides the first observation results regarding collagen type influence. With higher water solubility and more charged amino acids than type II, collagen type I intertwines with surimi myofibrillar proteins better to induce higher exposure of protein functional domains, more sufficient conformational changes of myosin and greater formation of chemical forces among proteins. These enhancements accelerate the gelation rate, leading to a well-stabilized surimi gel. The collagen I-containing surimi gels show more compact structures with uniformly distributed smaller pores than those containing collagen II, thereby providing the final products with higher water holding capacity and better textural profiles. As such, the surimi gel fortification performance of collagen I and the well-elucidated collagen-myofibrillar protein interaction mechanism will guide the further exploitation of collagen as an effective additive in the food industry.

Preparation of Gelatin from Broiler Chicken Stomach Collagen

With the increasing consumption of poultry meat around the world, the use of chicken stomachs as a source of collagen is being offered. The objective of this study was to extract gelatin from the stomachs of broiler chickens and to estimate their gel strength, ash content, viscosity, gelling point, melting point, clarity and digestibility. An innovative biotechnological method based on the conditioning of collagen with a microbial endoproteinase (Protamex^®) and hot-water extraction was used to control the chemical and thermal denaturation process of collagen to prepare gelatin. The experiments were planned using a Taguchi design, 2 factors at 3 levels; factor A for the amount of proteolytic enzyme (0.10, 0.15 and 0.20%) and factor B for the extraction temperature (55.0, 62.5 and 70.0 °C). Data were statistically processed and analyzed at a significance level of 95%. The gelatin yield averaged 65 ± 8%; the gel strength ranged from 25 ± 1 to 439 ± 6 Bloom, the viscosity from 1.0 ± 0.4 to 3.40 ± 0.03 mPa·s, gelling point from 14.0 ± 2.0 to 22.0 ± 2.0 °C, melting point from 28.0 ± 1.0 to 37.0 ± 1.0 °C. The digestibility of gelatin was 100.0% in all samples; the ash content was very low (0.44 ± 0.02-0.81 ± 0.02%). The optimal conditions for the enzymatic treatment of collagen from chicken stomachs were achieved at a higher temperature (70.0 °C) and a lower amount of enzyme (0.10-0.15%). Conditioning chicken collagen with a microbial endoproteinase is an economically and environmentally friendly processing method, an alternative to the usual acid- or alkaline-based treatment that is used industrially. The extracted products can be used for food and pharmaceutical applications.

The Texture Change of Chinese Traditional Pig Trotter with Soy Sauce during Stewing Processing: Based on a Thermal Degradation Model of Collagen Fibers

In order to clarify the influence of the thermal degradation of collagen fibers on the texture profile analysis (TPA) parameters of pig trotter stewed with soy sauce (PTSWSS), TPA (springiness, chewiness, hardness, and gumminess), the secondary structures, the cross-linkage, decorin (DCN) and glycosaminoglycan (GAG) levels, and the histochemical morphology of collagen fibers during the stewing process (0, 30, 60, 120 min) were assessed. The springiness and hardness increased after 30 min of stewing, along with the denaturation of collagen proteins. TPA parameters improved with the prolonged stewing times of 60 and 120 min, along with the ultra-structural dissolution of collagen fibers, and a substantial reduction in cross-linkage, DCN, and GAG levels, and the unfolded triple-helix structure. This study concluded that the TPA parameters of PTSWSS were dependent on the stewing time, and that the improvement in TPA parameters with longer stewing time could primarily be attributed to the thermal degradation of collagen fibers.