Determination of the influence of high pressure processing on calf rennet using response surface methodology: Effects on milk coagulation

S-Allyl cysteine in garlic (Allium sativum): Formation, biofunction, and resistance to food processing for value-added product development

S-allyl cysteine (SAC), which is the most abundant bioactive compound in black garlic (BG; Allium sativum), has been shown to have antioxidant, anti-apoptotic, anti-inflammatory, anti-obesity, cardioprotective, neuroprotective, and hepatoprotective activities. Sulfur compounds are the most distinctive bioactive elements in garlic. Previous studies have provided evidence that the concentration of SAC in fresh garlic is in the range of 19.0-1736.3 μg/g. Meanwhile, for processed garlic, such as frozen and thawed garlic, pickled garlic, fermented garlic extract, and BG, the SAC content increased to up to 8021.2 μg/g. BG is an SAC-containing product, with heat treatment being used in nearly all methods of BG production. Therefore, strategies to increase the SAC level in garlic are of great interest; however, further knowledge is required about the effect of processing factors and mechanistic changes. This review explains the formation of SAC in garlic, introduces its biological effects, and summarizes the recent advances in processing methods that can affect SAC levels in garlic, including heat treatment, enzymatic treatment, freezing, fermentation, ultrasonic treatment, and high hydrostatic pressure. Thus, the aim of this review was to summarize the outcomes of treatment aimed at maintaining or increasing SAC levels in BG. Therefore, publications from scientific databases in this field of study were examined. The effects of processing methods on SAC compounds were evaluated on the basis of the SAC content. This review provides information on the processing approaches that can assist food manufacturers in the development of value-added garlic products.

Advances in research on calf rennet substitutes and their effects on cheese quality

Milk coagulation is an important step in cheese production, and milk-clotting enzymes (MCEs) play a major role in this process. Calf rennet is the most widely used MCE in the cheese industry. The use of calf rennet substitutes is becoming necessary due to the limited availability of calf rennet and the increase in cheese consumption. The objective of this review is to summarize the latest findings on calf rennet substitutes (animal MCEs, plant-derived MCEs, recombinant MCEs and microbial MCEs) and their application in cheese production. Special emphasis has been placed on aspects of the effects of these substitutes on hydrolysis, functional peptides, cheese variety and cheese yield. The advantages and disadvantages of different calf rennet substitutes are discussed, in which microbial MCEs have the advantages of less expensive production, greater biochemical diversity, easier genetic modification, etc. In particular, some of these MCEs have suitable characteristics for cheese production and are considered to be the most potential calf rennet substitutes. Moreover, challenges and future perspectives are presented to provide inspiration for the development of excellent calf rennet substitutes.

Structure and shelf stability of milk protein gels created by pressure-assisted enzymatic gelation

In this work, pressure-assisted enzymatic gelation was applied to milk proteins, with the goal of enhancing the structure and stability of pressure-created milk protein gels. High-pressure processing (HPP) at 600 MPa, 3 min, and 5°C was applied to milk protein concentrate (MPC) samples of 12.5% protein concentration, both in the absence and in the presence of calf chymosin [up to 60 IMCU (international milk-clotting units)/kg of milk] or camel chymosin (up to 45 IMCU/kg of milk). Gel hardness, water-holding capacity, and degree of proteolysis were used to assess network strength and shelf stability. The processing trials and all measurements were conducted in triplicate. Statistical analyses of the data were performed by ANOVA, at a 95% confidence level. After HPP treatment, we observed significant structural changes for all samples. Pressurization of MPC, with or without chymosin addition, led to extensive protein aggregation and network formation. The strength of HPP-created milk protein gels without chymosin addition, as measured by the elastic modulus (G'), had a value of 2,242 Pa. The value of G' increased with increasing chymosin concentration, reaching as high as 4,800 Pa for samples with 45 IMCU/kg of camel chymosin. During 4 wk of refrigerated storage, the HPP and chymosin MPC gels maintained higher gel hardness and better structural stability compared with HPP only (no chymosin) MPC gels. The water-holding capacity of the gels without chymosin remained at 100% during 28 d of refrigerated storage. The HPP and chymosin MPC gels had a lower water-holding capacity (91-94%) than the HPP-only counterparts, but their water-holding capacity did not decrease during storage. Overall, these findings demonstrate that controlled, fast structural modification of high-concentration protein systems can be obtained by HPP-assisted enzymatic treatment, and the created gels have a strong, stable network. This study provides insights into the possibility of using HPP for the development of milk-protein-based products with novel structures and textures and long refrigerated shelf life, along with the built-in safety imparted by the HPP treatment.

Impact of high-pressure treatment on casein micelles, whey proteins, fat globules and enzymes activity in dairy products: a review

The quality and safety of food products are the two factors that most influence the demands made by consumers. Contractual food sterilization and preservation methods often result in unfavorable changes in functional properties of foods. High-pressure processing (HPP) (50-1000 MPa) is a non-thermal preservation technique, which can effectively reduce the activity of spoilage and pathogenic microorganisms with minimal impact on the functional and nutritional properties of food. Comprehensive inquires have disclosed the potential profits of HPP as an alternative to heat treatments by affecting the structure of milk components, particularly proteins and fats. The present paper aims to investigate the effects of HPP on milk components including fats, casein, whey proteins, enzymes, and minerals, as well as on the industrial production of milk and dairy products including cheese, yogurt, ice cream, butter, cream, and probiotic dairy products. HPP allows to extend shelf life of products without the use of additives, meeting current consumer demands. The assurance of microbial safety and the production of food products with minimal changes in quality characteristics (organoleptic, nutritional, and rheological properties) are among its main effects. In addition, the nutritional value of HPP-treated dairy products is also preserved.

A strategy for promoting γ-glutamyltransferase activity and enzymatic synthesis of S-allyl-(L)-cysteine in aged garlic via high hydrostatic pressure pretreatments

S-allyl-(L)-cysteine (SAC) is a bioactive compound within garlic. Its level is low since SAC formation is impeded by the cellular structure of garlic. This study investigates the effect of high hydrostatic pressure (HHP) pretreatment on SAC formation in garlic aged at 40 °C for 10 days. Results showed that HHP could enhance γ-glutamyltransferase (γ-GTP) activity, damage the cellular structure of garlic and increase SAC content in aged garlic by about 7-10 times, depending on the processing parameters. HHP processing at 300 MPa for 15 min provided the optimal conditions for enhancing γ-GTP activity (45%) and promoting SAC formation (from 0.51 ± 0.01 to 5.60 ± 0.22 mg/g dry weight). It was also found that HHP could induce the greening and browning of aged garlic. As such, we consider that HHP technology is a promising technique to produce aged black garlic products with higher amounts of bioactive compounds.

Biophysical evaluation of milk-clotting enzymes processed by high pressure

High pressure processing (HPP) is able to promote changes in enzymes structure. This study evaluated the effect of HP on the structural changes in milk-clotting enzymes processed under activation conditions for recombinant camel chymosin (212MPa/5min/10°C), calf rennet (280MPa/20min/25°C), bovine rennet (222MPa/5min/23°C), and porcine pepsin (50MPa/5min/20°C) and under inactivation conditions for all enzymes (600MPa/10min/25°C) including the protease from Rhizomucor miehei. In general, it was found that the HPP at activation conditions was able to increase the intrinsic fluorescence of samples with high pepsin concentration (porcine pepsin and bovine rennet), increase significantly the surface hydrophobicity and induce changes in secondary structure of all enzymes. Under inactivation conditions, increases in surface hydrophobicity and a reduction of intrinsic fluorescence were observed, suggesting a higher exposure of hydrophobic sites followed by water quenching of Trp residues. Moreover, changes in secondary structure were observed (with minor changes seen in Rhizomucor miehei protease). In conclusion, HPP was able to unfold milk-clotting enzymes even under activation conditions, and the porcine pepsin and bovine rennet were more sensitive to HPP.