Proteomics-guided isolation of a novel serine protease with milk-clotting activity from tamarillo (Solanum betaceum Cav.)

Tamarillo is widely grown in Yunnan Province, China, and has been found that it can be used in cheese-making with a distinctive fruity flavour. However, this primary component responsible for curdling milk remains unclear. This study aimed to identify the main component in tamarillo responsible for curdling milk using proteomics and ammonium sulfate (AS) precipitation. Herein, 3199 proteins were identified in tamarillo, of which 546 exhibited hydrolase activity. In particular, a novel serine protease with milk-clotting activity (MCA) and a molecular weight of 79.1 kDa, named "MCP746", was isolated from tamarillo. The milk-clotting proteases (MCPs) from tamarillo exhibited the highest MCA at 80 °C and stability under incubation temperatures below 70 °C, pH range of 5-8, and NaCl concentrations below 1 mol/L. This study revealed that serine protease is the primary MCPs of tamarillo along with a characterization of its milk-clotting characteristics, providing valuable insights into its potential application in cheese-making.

Determination of insoluble calcium content in Cheddar, feta, Juustoleipa, and mozzarella cheeses using acid-base buffering curves

The amount of colloidal calcium phosphate (CCP) complex associated with caseins (insoluble [INSOL] Ca) determines the body, texture, flavor, and breakdown of cheese constituents during aging. The continuous pH decline during cheesemaking because of lactic acid fermentation results in solubilization of INSOL Ca. Measuring INSOL Ca in such a dynamic and wide range pH system (6.6 to 5.3) is challenging. The purpose of this study was to test utility of an acid-base auto-titration method in differentiating INSOL Ca content in cheeses with a wide range of pH (i.e., Juustoleipa 6.6, mozzarella 5.6, Cheddar 5.3, feta 4.8) and also to understand the relationship between pH, protein content, and INSOL Ca. A positive relationship was obtained for pH (R2 = 0.62) and protein content (R2 = 0.85) with INSOL Ca, suggesting concomitant release of CCP content at lower pH values and association of higher amount of CCP with higher protein content. Despite having a pH slightly closer to mozzarella (pH 5.56), Cheddar cheese (pH 5.25) had more INSOL Ca (0.67%) owing to the highest amount of protein (26%) and low moisture content (33%). Feta had the lowest amount of INSOL Ca (0.15%) owing to a low pH (4.79), higher moisture content (55%), and low protein content (14%). Juustoleipa had the highest percentage of INSOL Ca out of total Ca (88%) due to higher pH (6.62) and more intact casein. It was evident that the acid-base titration method was able to differentiate INSOL Ca between different types of cheeses with varying pH and protein content. Findings of this work will help tracking the proportion of INSOL Ca at various stages of cheesemaking and understanding kinetics of INSOL Ca solubilization and its role in causing pH variation in the early stage of cheese ripening.

Production and functional characteristics of low-sodium high-potassium soy protein for the development of healthy soy-based foods

The plant-based products that are mainly produced by soy protein isolate (SPI) present significantly higher sodium (Na) content than the corresponding animal-based products. Accordingly, the production of low-sodium soy protein ingredients becomes a challenging task. For this purpose, alternative soy fractionation processes were investigated, and the use of KOH as the replacement for NaOH has been established to produce soy protein fractions (SPFs). The obtained MF-K contained 0.2 mg sodium and 24 mg potassium per 100 g of fraction, which was 3 % of the sodium content in the SPI, and the potassium content was over 10 times higher than SPI. Besides, using KOH increased the protein content of SPFs by almost 7 %, as well as their water holding capacity (WHC) and thermal stability; however, the yields of SPFs were dropped by around 4-8 % while the protein solubility of SPFs was reduced companied with the application of KOH. The fractionation processes mainly affected the protein composition, powder morphology, and viscosity of SPFs, while the sodium and potassium content showed limited impacts on the variations. Overall, the application of KOH during different fractionation procedures provided the possibility to produce low-sodium high‑potassium soy protein ingredients for the development of healthy soy-based foods.

Influence of salt concentration on microbial growth in Kashkaval cheese

The aim of the present study was to evaluate the influence of NaCl concentration on the microflora in Kashkaval cheese produced from cow’s milk. Three cheese samples were obtained - with low (0.7%), medium (1.5%), and standard (3.1%) content of NaCl. Microbiological analyses were performed on the 1st, 15th, 30th, and 45th d of cheese ripening. It was established that the NaCl content has a significant (p < 0.05) influence on the growth and activity of the microflora in studied samples. It has been observed that the total Lactic acid bacteria (LAB) increased up to 30 d during ripening, after which their concentration decreased. A higher LABs count of samples with 0.7% NaCl and 1.5% NaCl in comparison with those containing 3.1% NaCl was found. At the same time, the variations in the salt content do not have a significant (p > 0.05) impact on the growth of Psychrotrophic bacteria, while in samples with a low salt content, the growth of Yeast and Molds was more intense. The data obtained in the present study showed that the concentration of NaCl is important for the regulation of activity of microbiological processes during the ripening of the Kashkaval cheese samples.

Quark Cheese Processed by Dense-Phase Carbon Dioxide: Shelf-Life Evaluation and Physiochemical, Rheological, Microstructural and Volatile Properties Assessment

Dense-phase carbon dioxide (DPCD), a novel non-thermal processing technology, has attracted extensive attention due to its excellent performance in food sterilization and enzyme inactivation without quality deterioration. In this work, we aimed to extend the shelf life of quark cheese with DPCD and explore the effect of DPCD treatment as well as storage time on the quality of quark cheese. The sterilization parameters were optimized by means of orthogonal experiments, and the physiochemical, rheological, microstructural and volatile properties of cheese were investigated. The optimal DPCD treatment (20 MPa, 45 min, 55 °C) successfully extended the shelf life of quark cheese due to its inhibition effect on yeast and was able to slow down the proteolysis and alterations in pH and color of cheese. Cheese processed using DPCD after 14-day storage even displayed similar rheological properties to the control at day 0, from which bound water significantly migrated during storage. Moreover, DPCD contributed to the retention of the volatile profile of cheese during storage. This study demonstrated that DPCD is a promising pasteurization technology for quark cheese to improve its quality stability during storage.

Metal organic framework-based antibacterial agents and their underlying mechanisms

Bacteria, as the most abundant living organisms, have always been a threat to human life until the development of antibiotics. However, with the wide use of antibiotics over a long time, bacteria have gradually gained tolerance to antibiotics, further aggravating threat to human beings and environmental safety significantly. In recent decades, new bacteria-killing methods based on metal ions, hyperthermia, free radicals, physical pricks, and the coordination of several multi-mechanisms have attracted increasing attention. Consequently, multiple types of new antibacterial agents have been developed. Among them, metal organic frameworks (MOFs) appear to play an increasingly important role. The unique characteristics of MOFs make them suitable multiple-functional platforms. By selecting the appropriate metastable coordination bonds, MOFs can act as reservoirs and release antibacterial metal ions or organic linkers; by constructing a porous structure, MOFs can act as carriers for multiple types of agents and achieve slow and sustained release; and by designing their composition and the pore structure precisely, MOFs can be endowed with properties to produce heat and free radicals under stimulation. Importantly, in combination with other materials, MOFs can act as a platform to kill bacteria effectively through the synergistic effect of multiple types of mechanisms. In this review, we focus on the recent development of MOF-based antibacterial agents, which are classified according to their antibacterial mechanisms.

The Effect of Salt Reduction and Partial Substitution of NaCl by KCl on Physicochemical, Microbiological, and Sensorial Characteristics and Consumers' Acceptability of Semi-Hard and Hard Lactose-Free Cow's Milk Cheeses

Increasing consumer demand for healthier foods prompts the development of cheeses reduced in salt. The aim of his study was to assess the effect of reducing the level of sodium chloride (NaCl) and their partial substitution by potassium chloride (KCl) on the biochemical, microbiological, and sensorial characteristics and consumer's acceptability of semi-hard and hard lactose-free cow's milk cheeses. To improve the possible lower salty taste or the development of bitter taste, the addition to yeast extract, as a flavor enhancer, was also checked. Different brining times and brine conditions were tested to obtain a reduction of >25% of salt with respect to conventional cheese. Reduced-salt cheeses were elaborated by reducing half the salting time used in conventional cheeses, and a ratio of 60 Na⁺:40 K⁺ was used to reduce Na concentration in substituted cheeses. The results obtained in this study show that the reduction of salt by both methods in semi-hard and hard lactose-free cheeses could be an alternative for the production of healthier and sensorial acceptable cheeses, without significantly affecting their physicochemical characteristics. The addition of yeast extract, as a flavor enhancer, increased the free amino acids (FAAs) levels but decreased the acceptability of cheeses.

Microbial community and functional prediction during the processing of salt production in a 1000-year-old marine solar saltern of South China

In Hainan Island, South China, a 1000-year-old marine saltern has been identified as an intangible cultural heritage due to its historical complicated salt-making techniques, whereas the knowledge about this saltern is extremely limited. Herein, DNA sequencing and biochemical technologies were applied to determine bacterial and fungal communities of this saltern and their possible functions during four stages of salt-making, i.e. seawater storage, mud solarization, brine concentrating, and solar crystallization. The results showed that both of bacterial and fungal communities were suffered from significant changes during processing of salt-making in Danzhou Ancient Saltern, whereas the richness and diversity of bacterial community dominated by Proteobacteria, Bacteroidota and Cyanobacteria was considerably greater than that of fungal community dominated by Ascomycota, Basidiomycota and Mortierellomycota. Additionally, the succession of bacterial community was closely associated with both of salt physicochemical properties (Na⁺, Cl^-, total phosphorus, total nitrogen, Ca²⁺ and Mg²⁺) and bacteria themselves, whereas fungal community was more closely associated with physicochemical properties than fungi themselves. Importantly, Cyanobium_PCC-6307, Synechococcus_CC9902, Marinobacter, Prevotella and Halomonas as dominant bacterial genera respectively related to the metabolisms of amino acid, carbohydrate, terpenoids/polyketides, lipid and nucleotide were correlated with salt flavors. Saprophytic and saprotroph-symbiotroph fungi dominated by Aspergillus, Mortierella, Amanita, Neocucurbitaria and Tausonia also played core roles in the formation of salt flavors including umami and sweet smells. These findings revealed the highly specified microbiome community in this 1000-year-old saltern that mainly selected by brine solarization on basalt platforms, which is helpful to explore the underlying mechanisms of traditional salt-making techniques and to explore the useful microbes for nowadays food, medicine and chemical industries.

Pequi (Caryocar brasiliense) Waste Extract as a Synergistic Agent in the Microbial and Physicochemical Preservation of Low-Sodium Raw Goat Cheese

The growth of spoilage and pathogenic bacteria during storage represents significant losses in marketing raw milk cheeses. Thus, reducing NaCl in these products is challenging, as sodium has a critical antimicrobial role. Despite advances in non-thermal technologies, the short shelf life still limits the availability of raw goat cheese. Thus, combined preservation methods can be promising because their synergies can extend shelf life more effectively. In this context, Principal Component Analysis (PCA) was applied to variables to investigate the effect of pequi waste extract (PWE), a native Brazilian fruit, combined with UV-C radiation (CEU) and vacuum packaging (CEV) on the preservation of low-sodium raw goat cheese. CEV samples had lower loadings for Staphylococcus subsp. and Enterobacteriaceae than other treatments in PC2, having a count's reduction up to 3-fold (P < 0.05) compared to vacuum alone. In contrast, CEU showed an increase of up to 1.2-fold on staphylococcal count compared to UV-C alone. Still, the addition of PWE to UV-C-treated cheeses resulted in 8.5% protein loss. Furthermore, PWE, especially in CEV, delayed post-acidification during storage. It made CEV up to 4.5 and 1.6-fold more stable for color and texture, respectively than vacuum alone. These data strongly suggest that PWE may be a novel and promising synergistic agent in the microbial and physicochemical preservation of low-sodium raw milk cheese when combined with the vacuum.

Comparison of growth and survival of single strains of Lactococcus lactis and Lactococcus cremoris during Cheddar cheese manufacture

Traditionally, starter cultures for Cheddar cheese are combinations of Lactococcus lactis and Lactococcus cremoris. Our goal was to compare growth and survival of individual strains during cheesemaking, and after salting and pressing. Cultures used were 2 strains of L. lactis (SSM 7605, SSM 7436) and 2 strains of L. cremoris (SSM 7136, SSM 7661). A standardized Cheddar cheese make procedure was used that included a 38°C cook temperature and salting levels of 2.0, 2.4, 2.8, 3.2, and 3.6% from which were selected cheeses with salt-in-moisture levels of 3.5, 4.5, and 5.5%. Vats of cheese were made using each strain on its own as biological duplicates on different days. Starter culture numbers were enumerated by plate counting during cheesemaking and after 6 d storage at 6°C. Flow cytometry with fluorescent staining by SYBR Green and propidium iodide was used to determine the number of live and dead cells in cheese at the different salt levels. Differences in cheese make times were strain dependent rather than species dependent. Even with correction for average culture chain length, cheeses made using L. lactis strains contained ∼4 times (∼0.6 log) more bacterial cells than those made using L. cremoris strains. Growth of the strains used in this study was not influenced by the amount of salt added to the curd. The higher pH of cheeses with higher salting levels was attributed to those cheeses having a lower moisture content. Based on flow cytometry, ∼5% of the total starter culture cells in the cheese were dead after 6 d of storage. Another 3 to 19% of the cells were designated as being live, but semipermeable, with L. cremoris strains having the higher number of semipermeable cells.

Effect of Salt Content Reduction on Food Processing Technology

Higher salt intake is associated with the risk of cardiovascular and kidney diseases, hypertension and gastric cancer. Salt intake reduction represents an effective way to improve people’s health, either by the right choice of food or by a reduction of added salt. Salt substitutes are often used and also herb homogenates are treated by high pressure technology. Salt reduction significantly influences the shelf life, texture, pH, taste, and aroma of cheese. The composition of emulsifying salts or starter cultures must be modified to enact changes in microbial diversity, protease activity and the ripening process. The texture becomes softer and aroma atypical. In bakery products, a salt reduction of only 20–30% is acceptable. Water absorption, dough development, length and intensity of kneading and stability of dough are changed. Gluten development and its viscoelastic properties are affected. The salt reduction promotes yeast growth and CO₂ production. Specific volume and crust colour intensity decreased, and the crumb porosity changed. In meat products, salt provides flavour, texture, and shelf life, and water activity increases. In this case, myofibrillar proteins’ solubility, water binding activity and colour intensity changes were found. The composition of curing nitrite salt mixtures and starter cultures must be modified.

Galactose-positive adjunct cultures prevent gas formation by Paucilactobacillus wasatchensis WDC04 in a model gas production test

Gas production by obligatory heterofermentative lactic acid bacteria such as Paucilactobacillus wasatchensis is a sporadic problem in Cheddar cheese and results in undesired slits and cracks in the cheese. Growth of Pa. wasatchensis is not rapid, which makes investigations of gas production difficult to consistently execute. A primary objective of this study was to develop a model gas production test that could be used to investigate the effect of galactose and ribose utilization on gas production by Pa. wasatchensis and determine whether galactose-fermenting adjunct cultures could prevent gas formation. Paucilactobacillus wasatchensis WDC04 was inoculated at 10¹ to 10⁶ cfu/mL into carbohydrate-restricted MRS broth containing different ribose and galactose levels and incubated for up to 21 d at 23°C. Gas production in the broth was detected using a Durham tube inverted on a 6-cm-long capillary tube; cells were enumerated at 4, 8, and 12 d; and residual galactose was also measured. Gas production was sporadic except for when 10⁵ cfu/mL of Pa. wasatchensis WDC04 was inoculated into broth containing 0.3% ribose and 0.7% galactose. In those tubes, gas production was consistently observed after 8-d incubation, by which time galactose levels had decreased to 0.15%. Co-inoculation of Pa. wasatchensis WDC04 with as few as 10³ cfu/mL of a lactose-negative galactose-positive adjunct culture (Pediococcus acidilactici 23F, Lacticaseibacillus paracasei UW4, or Lactobacillus helveticus 7995) resulted in galactose depletion by d 4 and no observable gas production by d 12. With less galactose available to the slower-growing Pa. wasatchensis WDC04, its growth was limited to 10⁸ cfu/mL when any of the adjunct cultures was co-inoculated, compared with 10⁹ cfu/mL when grown on its own. We concluded that galactose-fermenting adjunct cultures have potential for preventing unwanted gas production in cheese by competition for resources and especially by removing the 6-carbon galactose before it can be utilized for energy by an obligatory heterofermentative lactobacilli such as Pa. wasatchensis and produce carbon dioxide.

Reduced-sodium cheeses: Implications of reducing sodium chloride on cheese quality and safety

Sodium chloride (NaCl) universally well-known as table salt is an ancient food additive, which is broadly used to increase the storage stability and the palatability of foods. Though, in recent decades, use of table salt in foods is a major concern among the health agencies of the world owing to ill effects of sodium (Na) that are mostly linked to hypertension and cardiovascular diseases. As a result, food scientists are working to decrease the sodium content in food either by decreasing the rate of NaCl addition or by partial or full replacement of NaCl with other suitable salts like potassium chloride (KCl), calcium chloride (CaCl₂ ), or magnesium chloride (MgCl₂ ). However, in cheese, salt reduction is difficult to accomplish owing to its multifaceted role in cheese making. Considering the significant contribution in dietary salt intake (DSI) from cheese, researchers across the globe are exploring various technical interventions to develop reduced-sodium cheeses (RSCs) without jeopardizing the quality and safety of cheeses. Thus, the purpose of this study is to provide an insight of NaCl reduction on sensory, physicochemical, and technofunctional attributes of RSCs with an aim to explore various strategies for salt reduction without affecting the cheese quality and safety. The relationship between salt reduction and survival of pathogenic and spoilage-causing microorganisms and growth of RSCs microflora is also discussed. Based on the understanding of conceptual and applied information on the complex changes that occur in the development of RSCs, the quality and safety of RSCs can be accomplished effectively in order to reduce the DSI from cheese.

Effect of microwave sterilization on maturation time and quality of low-salt sufu

The objective of this study was to reduce the microorganism number and salt content in pehtze by microwave sterilization. The maturation time and quality of low-salt sufu were evaluated. The microorganism inactivation rate, moisture content and water activity of the pehtze, which was used for the growth of the starter culture, showed that 4,250 W for 30 s was suitable for the preparation of low-salt sufu. With regard to the physicochemical properties of sufu, 120-day sufu samples obtained by traditional high-salt (14%) fermentation and 75-day sufu samples obtained by low-salt (4%) fermentation met the standard requirements. With regard to the sensory characteristics of sufu, the taste and after taste scores of 75-day low-salt sufu samples were significantly higher than those of 120-day high-salt sufu samples (p < .05).The overall acceptance score of low-salt sufu samples also was higher than that of high-salt sufu samples. The contents of free amino acids and the profiles of typical flavor compounds partly explained the sensory quality and shorter ripening time of sufu manufactured. The total biogenic amine contents were reduced by 46%.

Determination of compositional quality and volatile flavor characteristics of radish-based Kimchi suitable for Chinese consumers and its correlation to consumer acceptability

In this study, two prototype radish-based kimchi were developed for Chinese consumer market. The major difference between these samples was the liquid used during the salting stage. Kimchi 1 was salted in soy sauce while Kimchi 2 was salted in saline water. The quality factor differences were observed in Brix (°Brix), salinity, and capsaicin levels (p < 0.05). The volatile flavor analysis revealed that a different flavor profile was noted between the two kimchi samples; however, this did not influence consumer acceptance. The overall liking scores for Kimchi 1 and Kimchi 2 were 6.2 and 6.1, respectively, based on a 9-pt hedonic scale (p > 0.05). Current work presented two different prototypes of radish-based Kimchi developed for Chinese consumers. Slight differences were observed between the two radish-based kimchi samples, yet these differences did not influence consumer hedonic responses.

The Influence of Various Chloride Salts to Reduce Sodium Content on the Quality Parameters of Şalgam (Shalgam): A Traditional Turkish Beverage Based on Black Carrot

Sodium chloride is essential in şalgam processing affecting the flavour and microbiological stability of the final product. However, reduction of sodium salt in şalgam beverage is essential due to consumers’ demand for low-sodium foods as well as recommendation of health authorities. NaCl was replaced both partially and totally by KCl and CaCl2 in the present study. Experimental design was established to investigate the effects of five different combinations (1.7% NaCl (control treatment); 0.85% NaCl–0.85% KCl; 0.85% NaCl–0.85% CaCl2; 0.85% KCl–0.85% CaCl2, and 0.56% NaCl–0.56% KCl–0.56% CaCl2) of chloride salts on microbiological, chemical, and sensory qualities of şalgam. Lactic acid bacteria (LAB) were present in populations ranging from 8.0 to 8.61 log cfu/mL while total yeasts were 6.89 to 7.12 log cfu/mL at the end of the process. The maximum number of LAB was detected in the fermentation employed NaCl + KCl salts combination. Regarding the microbiological profile, LAB growth was stimulated significantly in presence of KCl while yeast patterns were not linked to different salt treatments. The final values of total acidity (TA) and pH for şalgam were found between 7.40 and 8.71 g/L and 3.26–3.47, respectively. Concerning physicochemical attributes, pH decreased when CaCl2 increased while TA is higher in the presence of CaCl2. Şalgam juice fermented with 0.85% NaCl–0.85% KCl mineral salt combination received the best sensory results among the different salt substitutions. Results demonstrate that NaCl can be replaced in şalgam with KCl by 50%, without affecting the traditional taste of şalgam in order to meet consumers’ demand for low-sodium dietary intake.

Fluorescence spectroscopy coupled with independent components analysis to monitor molecular changes during heating and cooling of Cantal-type cheeses with different NaCl and KCl contents

BACKGROUND

Reduction of NaCl content of cheeses has received considerable attention by research during the past decades because of its health effects. Nonetheless, NaCl reduction is a challenge since it plays an important role in cheese quality, such as structure, texture and functional properties. Several methods were used to evaluate the effect of NaCl on these attributes. In this study, Cantal-type cheeses with different salts (NaCl and KCl) were analyzed for their structure at a molecular level and rheological properties during heating (20-60 °C) and cooling (60-20 °C). The structure was investigated by synchronous fluorescence spectroscopy (SFS) and the rheological properties by small-amplitude oscillatory test.

RESULTS

Independent components analysis (ICA) gave three independent components that were attributed to coenzyme/Maillard reaction products (IC1), tryptophan (IC2) and vitamin A (IC3). Signal proportions of each IC depicted information regarding the changes in those fluorophores with salts, heating and cooling. In addition, canonical correlation analysis (CCA) of the IC proportions and rheological measurements related modifications at a molecular level evaluated by fluorescence to cheese texture (0.34 < R² < 0.99).

CONCLUSION

This study demonstrated that SFS can monitor and characterize modification of Cantal-type cheeses at a molecular level, based on the analysis of the fluorescence spectra by ICA. The nature of correlation between signal proportions and the rheological parameters depicted that rheological attributes of cheeses observed at the macroscopic level can be derived from fluorescence spectra. © 2017 Society of Chemical Industry.

Putrescine production by Lactococcus lactis subsp. cremoris CECT 8666 is reduced by NaCl via a decrease in bacterial growth and the repression of the genes involved in putrescine production

The reduction of NaCl in food is a public health priority; high NaCl intakes have been associated with serious health problems. However, it is reported that reducing the NaCl content of cheeses may lead to an increase in the content of biogenic amines (BAs). The present work examines the effect of NaCl on the accumulation of putrescine (one of the BAs often detected at high concentration in cheese) in experimental Cabrales-like cheeses containing Lactococcus lactis subsp. cremoris CECT 8666, a dairy strain that catabolises agmatine to putrescine via the agmatine deiminase (AGDI) pathway. The genes responsible for this pathway are grouped in the AGDI cluster. This comprises a regulatory gene (aguR) (transcribed independently), followed by the catabolic genes that together form an operon (aguBDAC). Reducing the NaCl concentration of the cheese led to increased putrescine accumulation. In contrast, increasing the NaCl concentration of both pH-uncontrolled and pH-controlled (pH 6) cultures of L. lactis subsp. cremoris CECT 8666 significantly inhibited its growth and the production of putrescine. Such production appeared to be inhibited via a reduction in the transcription of the aguBDAC operon; no effect on the transcription of aguR was recorded. The present results suggest that low-sodium cheeses are at risk of accumulating higher concentrations of putrescine.