Production of volatile sulfur compounds in Cheddar cheese slurries

Novel Bacillus Milk-Clotting Enzyme Produces Diverse Functional Peptides in Semihard Cheese

Although rennet is one of the best choices for cheese manufacturing, its production cannot meet the growing demands of the cheese industry. Thus, new milk-clotting enzymes (MCEs) with similar or better properties as/than those of calf chymosin are needed urgently. Here, three MCEs, BY-2, BY-3, and BY-4, were mined by bioinformatic analysis and then expressed in and isolated from Escherichia coli. BY-4 had the highest milk-clotting activity/proteolytic activity (238.76) with enzyme properties similar to those of calf chymosin. BY-4 cheese had a composition, appearance, consistency/texture, and overall acceptability proximate to calf chymosin cheese. The EC₅₀ values of peptides extracted from BY-4 cheese for 2,2-diphenyl-1-picrylhydrazyl inhibition (antioxidant property), angiotensin-converting enzyme inhibition (antihypertensivity), and growth inhibition of liver cancer cells (antitumor property) were found to be 81, 49, and 238 μg/mL, respectively, which were 2.35, 2.59, and 2.12 folds higher than those of calf chymosin cheese. These results indicated the potential of BY-4 as a supplement to calf chymosin in cheese manufacturing, especially for functional and health care purposes.

Effect of Supplementation of Herd Diet with Olive Cake on the Composition Profile of Milk and on the Composition, Quality and Sensory Profile of Cheeses Made Therefrom

Simple Summary

Replacing conventional feed with waste biomass produced by crop-industrial processes can be a good practice for the sustainability of crop-livestock systems and an interesting solution for their disposal—as long as they maintain the quality of products. Considering the relationship between feeding management and qualitative profile in products of animal origin, the aim of our study was to assess the effect of dietary olive cake supplementation on nutritional quality, fatty acid composition, volatile and sensory profile of milk and the cheese produced by dairy cows. The experiment was carried out on eighty-four healthy dairy Friesian cows, divided into two homogenous groups. Animals were fed with a conventional diet (CTR group) and a conventional diet supplemented with dried olive cake (OC group). Data showed that olive cake utilization in the diet of lactating dairy cows may modify the quality of dairy products. The increased unsaturated fatty acids (oleic acid, vaccenic acid and CLA) and decreased SFA (short- and medium-chain fatty acids) suggest a positive role of olive cake in improving the nutritional and nutraceutical properties of the cheese. Moreover, the olive cake affected not only the volatile profile of the cheese, but also its appearance, smell and taste, which are associated with a higher score of acceptance.

Abstract

Aim of the present study was to assess the effect of dietary dried partially destoned olive cake supplement on nutritional quality and sensory profile of milk and cheese produced by dairy cows. The experiment was carried out on eighty-four healthy dairy Friesian cows divided into two homogenous groups. The control group (CTR) received a conventional diet, whereas the experimental group (OC) received a conventional diet supplemented with olive cake as 15% of DM. The trial lasted five months. Monthly, on individual milk samples, yield and physical-chemical parameters were determined. Milk was used for the artisanal cheese production. On 10 samples of cheese for each group, physical-chemical and fatty acid profile were determined. Electronic nose analysis and sensory evaluation were performed. Data were analyzed by ANOVA. The diet affected (p < 0.05) the milk yield, exclusively in September. Yield and quality of cheese of OC group after 60 d of ripening showed higher (p < 0.05) yield, moisture and fat content, lower (p < 0.05) pH, protein, salt and ash content, higher (p < 0.01) MUFA and PUFA and CLA content, lower (p < 0.05) SFA, higher (p < 0.01) UFA/SFA and hypocholesterolemic/hypercholesterolemic ratios, better (p < 0.01) atherogenic and thrombogenic indices. Data show dietary olive cake supplementation in lactating dairy cows improves nutritional and nutraceutical properties of cheese, volatile profile and level of assessors’ acceptance.

Methionine metabolism: major pathways and enzymes involved and strategies for control and diversification of volatile sulfur compounds in cheese

For economical reasons and to accommodate current market trends, cheese manufacturers and product developers are increasingly interested in controlling cheese flavor formation and developing new flavors. Due to their low detection threshold and diversity, volatile sulfur compounds (VSCs) are of prime importance in the overall flavor of cheese and make a significant contribution to their typical flavors. Thus, the control of VSCs formation offers considerable potential for industrial applications. This paper gives an overview of the main VSCs found in cheese, along with the major pathways and key enzymes leading to the formation of methanethiol from methionine, which is subsequently converted into other sulfur-bearing compounds. As these compounds arise primarily from methionine, the metabolism of this amino acid and its regulation is presented. Attention is focused in the enzymatic potential of lactic acid bacteria (LAB) that are widely used as starter and adjunct cultures in cheese-making. In view of industrial applications, different strategies such as the enhancement of the abilities of LAB to produce high amounts and diversity of VSCs are highlighted as the principal future research trend.

Review. Sulfur-containing volatile compounds in seafood: occurrence, odorant properties and mechanisms of formation

An inventory of the most part of sulfur-containing volatile compounds (SCVCs) present in seafood was carried out. These molecules constitute key compounds to understand and improve seafood quality. According to their nature, concentration and environmental parameters (temperature), they can move the overall seafood odor from desirable to rotten. Sulfury odors can also indicate problems in sanitary quality. Thus, it is essential to monitor the generation of these compounds to better control the organoleptic and sanitary quality of seafood. SCVC were divided in two categories: aliphatic compounds and cyclic compounds. Among cyclic SCVC, several families of compounds can be distinguished as thiophenes, thiazoles and their respective derivatives. The main pathways of formation of SCVC in seafood are investigated in order to better understand their presence in seafood aroma. Microbial mediated enzymatic reactions are mainly implied in the generation of aliphatic SCVC whereas Maillard reactions are involved in the generation of cyclic SCVC. A small part of SCVC could also derive from the environment by direct bioaccumulation of S-containing molecules or precursors. Then, the occurrence of SCVC in seafood is discussed according to the extraction methods, analysis methods - sometimes olfactometric methods and the species - the state and the average biochemical composition of the seafood matrix in which they were recovered. Finally, among the identified SCVC, the odorant properties of odor-active volatile compounds were investigated. Aromatic notes and odorant thresholds for odorant SCVC of seafood aroma are listed. Both pathways of formation and lists of SCVC linked to their odorant properties constitute important indicators to optimise seafood quality from an organoleptic and sanitary point of view.

Heterologous production of methionine-gamma-lyase from Brevibacterium linens in Lactococcus lactis and formation of volatile sulfur compounds

The conversion of methionine to volatile sulfur compounds (VSCs) is of great importance in flavor formation during cheese ripening and is the focus of biotechnological approaches toward flavor improvement. A synthetic mgl gene encoding methionine-gamma-lyase (MGL) from Brevibacterium linens BL2 was cloned into a Lactococcus lactis expression plasmid under the control of the nisin-inducible promoter PnisA. When expressed in L. lactis and purified as a recombinant protein, MGL was shown to degrade L-methionine as well as other sulfur-containing compounds such as L-cysteine, L-cystathionine, and L-cystine. Overproduction of MGL in recombinant L. lactis also resulted in an increase in the degradation of these compounds compared to the wild-type strain. Importantly, gas chromatography-mass spectrometry analysis identified considerably higher formation of methanethiol (and its oxidized derivatives dimethyl disulfide and dimethyl trisulfide) in reactions containing either purified protein, whole cells, or cell extracts from the heterologous L. lactis strain. This is the first report of production of MGL from B. linens in L. lactis. Given their significance in cheese flavor development, the use of lactic acid bacteria with enhanced VSC-producing abilities could be an efficient way to enhance cheese flavor development.

Volatile sulphur compounds in UHT milk

Several volatile sulphur compounds have been detected in raw and processed milk. These are hydrogen sulphide, methanethiol, carbonyl sulphide, dimethyl sulphide, carbon disulphide, dimethyl disulphide, dimethyl trisulphide, dimethyl sulphoxide, and dimethyl sulphone. Many of these increase in milk during heat processing and are associated with the cooked flavor of heat-treated milks, particularly UHT and sterilized milk. Several researchers have attempted to explain the origin of these volatiles in both raw and processed milk, and how to reduce the associated cooked flavor that has a negative impact on consumer acceptability of processed milk. These compounds are difficult to detect and analyze due to their high volatility, sensitivity to oxidation and heat, and in some cases, their very low concentrations. However, methods of detection and quantification have improved in recent years. Pre-concentration methods such as solid phase microextraction (SPME) together with gas chromatography equipped with sulphur-selective detectors now enable low concentrations of these compounds to be analyzed. In this review, methods of extraction and analyzes of these volatile sulphur compounds are compared, and their occurrence in milk is reviewed.

Review of the toxicology of carbonyl sulfide, a new grain fumigant

Carbonyl sulfide (COS) is a new grain fumigant which has been developed to replace methyl bromide, being phased out due to its ozone depletion properties, and to supplement phosphine gas which is experiencing increased insect resistance. Treatment of commodities with COS, a highly effective fumigant, results in residues that are near or indistinguishable to natural background levels of this compound. COS is a naturally occurring gas, being the predominant sulfur moiety in the atmosphere, occurs naturally in food and is a normal by-product of mammalian aerobic metabolism. COS has low acute inhalational toxicity but with a steep dose response curve; COS is neither genotoxic nor a developmental toxicant but does reversibly impair male fertility. Prolonged, repeated exposure to COS is likely to present similar neurotoxicity hazards to that of the structurally and toxicologically related compound carbon disulfide. Although the occupational risks presented by COS as a fumigant of bulk grain are significant, these are, as they have been for a considerable time for phosphine and methyl bromide, manageable by good occupational safety practices. Consideration may need to be given to scrubbing of ventilated COS and its breakdown product hydrogen sulfide, at the completion of fumigation to minimise worker and bystander exposure. In terms of classical regulatory toxicology studies, the available database for COS is deficient in many aspects and registration in most jurisdictions will depend on sound scientific argument built upon the totality of the existing scientific data as there are strong arguments supporting the registration of this compound.

Fatty acid production from amino acids and alpha-keto acids by Brevibacterium linens BL2

Low concentrations of branched-chain fatty acids, such as isobutyric and isovaleric acids, develop during the ripening of hard cheeses and contribute to the beneficial flavor profile. Catabolism of amino acids, such as branched-chain amino acids, by bacteria via aminotransferase reactions and alpha-keto acids is one mechanism to generate these flavorful compounds; however, metabolism of alpha-keto acids to flavor-associated compounds is controversial. The objective of this study was to determine the ability of Brevibacterium linens BL2 to produce fatty acids from amino acids and alpha-keto acids and determine the occurrence of the likely genes in the draft genome sequence. BL2 catabolized amino acids to fatty acids only under carbohydrate starvation conditions. The primary fatty acid end products from leucine were isovaleric acid, acetic acid, and propionic acid. In contrast, logarithmic-phase cells of BL2 produced fatty acids from alpha-keto acids only. BL2 also converted alpha-keto acids to branched-chain fatty acids after carbohydrate starvation was achieved. At least 100 genes are potentially involved in five different metabolic pathways. The genome of B. linens ATCC 9174 contained these genes for production and degradation of fatty acids. These data indicate that brevibacteria have the ability to produce fatty acids from amino and alpha-keto acids and that carbon metabolism is important in regulating this event.

Identification and functional analysis of the gene encoding methionine-gamma-lyase in Brevibacterium linens

The enzymatic degradation of L-methionine and subsequent formation of volatile sulfur compounds (VSCs) is believed to be essential for flavor development in cheese. L-methionine-gamma-lyase (MGL) can convert L-methionine to methanethiol (MTL), alpha-ketobutyrate, and ammonia. The mgl gene encoding MGL was cloned from the type strain Brevibacterium linens ATCC 9175 known to produce copious amounts of MTL and related VSCs. The disruption of the mgl gene, achieved in strain ATCC 9175, resulted in a 62% decrease in thiol-producing activity and a 97% decrease in total VSC production in the knockout strain. Our work shows that L-methionine degradation via gamma-elimination is a key step in the formation of VSCs in B. linens.

Amino acid catabolism in cheese-related bacteria: selection and study of the effects of pH, temperature and NaCl by quadratic response surface methodology

AIMS

To screen the cystathionine lyase and L-methionine aminotransferase activities of cheese-related bacteria (lactococci, non-starter lactobacilli and smear bacteria) and to determine the individual and interactive effects of temperature, pH and NaCl concentration on selected enzyme activities.

METHODS AND RESULTS

A subcellular fractionation protocol and specific enzyme assays were used, and a quadratic response surface methodology was applied. The majority of the strains, 21 of 33, had detectable cystathionine lyase activity which differed in the specificity. Aminotransferase activity on L-methionine was observed in only three strains. The cystathionine lyase activities of Lactobacillus reuteri DSM20016, Lactococcus lactis subsp. cremoris MG1363, Brevibacterium linens 10 and Corynebacterium ammoniagenes 8 and the L-methionine aminotransferase activity of Lact. reuteri DSM20016 had temperature and pH optima of 30-45 degrees C, and 7.5-8.0, respectively. As shown by the quadratic response surface methodology these enzymes retained activities in the range of temperature, pH and NaCl concentration which characterized the cheeses from which the bacteria originated.

CONCLUSION

The enzyme activities may have a role in flavour development during cheese ripening.

SIGNIFICANCE AND IMPACT OF THE STUDY

The findings of this work contribute to the knowledge about the amino acid catabolic enzymes in order to improve cheese ripening.

Diversity of sulfur compound production in lactic acid bacteria

Volatile sulfur compounds such as methanethiol, dimethyl disulfide, dimethyl trisulfide, and hydrogen sulfide constitute an important fraction of Cheddar cheese flavor. These compounds are products of the catabolism of methionine and cysteine by bacteria in the cheese matrix. The objectives of this study were to examine the levels and types of volatile sulfur compounds produced from methionine by lactic acid bacteria frequently used in cheese making and to investigate cystathionine degrading activity, which may be responsible for the liberation of these compounds. Gas chromatography with headspace sampling was used to determine volatile sulfur compounds (VSC) produced by whole cells of 24 strains of lactobacilli and 13 strains of lactococci incubated with methionine. Total VSC production varied widely in the species and subspecies tested. Nearly all strains produced VSC from methionine, but the enzyme responsible for this activity remains unclear. Cystathionine-degrading ability and the effect of methionine concentration on this ability of some of the strains was investigated. Increasing the concentrations of methionine inhibited the cystathionine-degrading ability of lactococci, but not of lactobacilli. Lactococci were found to require methionine for growth, while lactobacilli required both methionine and cysteine. Because of the low level of cystathionine-degrading activity in lactobacilli and the inhibition of this activity by methionine in lactococci, VSC production is likely due to enzymes other than cystathionine beta- and gamma-lyase in whole cells.

Biotechnological approaches to the understanding and improvement of mature cheese flavour

There have been important milestones in biotechnological practice that have led to the determination and production of superior cheese flavours. Within the past year, the use of gas chromatographic techniques and sensory methodologies has been optimised by several groups in efforts to evaluate the organoleptic properties of a number of mature cheeses. The hydrolysis of milk caseins, small peptides, free amino acids and fatty acids, and the generation of sulfur-containing compounds are uniformly assumed to result in the formation of specific cheese aromas. Giant strides have been taken in molecular technology to aid the dissection and exploitation of the metabolic pathways that lead to the formation of these flavour constituents. Specific advances in molecular technology have included metabolic engineering of lactic acid bacteria for enhanced flavour development.