Starter bacteria are the prime agents of lipolysis in cheddar cheese

To assess the contribution of starter lactic acid bacteria (LAB) to lipolysis in Cheddar cheese, the evolution of free fatty acids (FFAs) was monitored in Cheddar cheeses manufactured from pasteurized milks with or without starter. Starter-free cheeses were acidified by a combination of lactic acid and glucono-delta-lactone. Starter cultures were found to actively produce FFAs in the cheese vat, and mean levels of FFAs were significantly higher in starter cheeses over ripening. The contribution of nonstarter LAB toward lipolysis appears minimal, especially in starter-acidified cheeses. It is postulated that the moderate increases in FFAs in Cheddar cheese are primarily due to lack of access of esterase of LAB to suitable lipid substrate. The results of this study indicate that starter esterases are the primary contributors to lipolysis in Cheddar cheese made from good quality pasteurized milk.     

Aerobic biodegradation of precoagulated cheese whey wastewater

Prior to the application of an aerobic biological process, cheese whey wastewater has been pretreated by means of a precipitation stage by adding either NaOH or CaOH2. Both precipitating agents reduce roughly 50% of the raw wastewater chemical oxygen demand (COD). The sludge generated in the prestage shows acceptable settling properties, although solids from the CaOH2-treated effluent are better separated from the liquid bulk than those formed in NaOH-processed wastewater. In both situations, the presedimentation stage renders a supernatant more prone to biodegradation than the untreated effluent. The previous statement is corroborated by the determination of some biological kinetic parameters. Under the operating conditions used in this work, sludge generation after the biological process is reduced to a minimum. The sludge generated shows good settling properties, especially for those experiments in which CaOH2 has previously been added.     

Flavor enhancement of reduced fat cheddar cheese using an integrated culturing system

Mild cheese flavor in reduced fat Cheddar cheese was enhanced by using an integrated starter culture system. Three cultures, Lactococcus lactis subsp. cremoris SK11, L. lactis subsp. lactis biovar. diacetylactis JVI, and Lactobacillus casei 7A, were carefully selected to obtain a nonbitter, mildly acid, buttery flavored cheese. Cheeses were produced from all possible combinations of these cultures with the constraint that L. lactis subsp. cremoris SK11 was used as the primary acid-producing culture. Cheeses made with SK11 were compared to cheeses produced using an L. lactis subsp. cremoris commercial starter culture. Cheeses were ripened for 150 days and periodically sampled for chemical, microbiological, and sensory analysis. Cheeses produced with L. lactis subsp. cremorisSK11 had substantially lower bitterness intensity than the cheeses produced with commercial starter culture. L. lactis subsp. lactis biovar. diacetylactis JVI significantly increased diacetylacetoin and acetate concentrations. Sensory results indicate that these cheeses had increased buttery (diacetyl) flavor.     

Influence of a probiotic adjunct culture of Enterococcus faecium on the quality of cheddar cheese

Cheddar cheese has previously been shown to be an effective vehicle for delivery of viable cells of a probiotic Enterococcus faecium strain to the gastrointestinal tract. The particular strain, E. faecium PR88, has proven efficacy in the treatment of irritable bowel syndrome, and in this study it was evaluated for suitability as a starter adjunct for Cheddar cheese manufacture. When added to cheesemilk at an inoculum of 2 x 10(7) cfu/mL, the enterococcal adjunct maintained viability in Cheddar cheese at levels of up to 3 x 10(8) cfu/g during 9 months of ripening. Increased proteolysis and higher levels of some odor-active volatile compounds were observed in Cheddar cheeses containing the PR88 adjunct compared with the control throughout the ripening period. In addition, the enterococcal adjunct strain did not affect cheese composition. Although sensory evaluation showed no significant difference in flavor/aroma and body/texture scores between control and experimental cheeses, repeated comments by the commercial grader consistently described the cheeses containing PR88 as 'more advanced than the control' and as having 'better flavor'. These findings indicate that the presence of the PR88 adjunct strain in Cheddar cheese at levels of >/=10(8) cfu/g may positively influence Cheddar flavor.     

Straightforward process for removal of milk fat globule membranes and production of fat-free whey protein concentrate from cheese whey

A straightforward method for the separation of milk fat globule membrane (MFGM) and production of fat-free whey protein concentrate/isolate from cheese whey has been developed. Lowering of the conductivity of the whey from its initial value of about 5600 μS cm(-1) to about 2000-500 μS cm(-1) via diafiltration with water caused selective precipitation of MFGM when incubated for 30 min at pH 4.2 and 35 °C. The whey proteins remained soluble in the supernatant under these conditions. Experimental evidence suggested that precipitation of MFGM at pH 4.2 was not due to a nonspecific effect of lowering of the conductivity of the whey but due to the specific effect of removal of Ca2+ from the whey. The lipid content of whey protein isolate obtained by this process was <0.2%, and the protein loss was <14%. The method provides an industrially feasible process for the production of fat-free whey protein concentrate/isolate. The MFGM, which is reported to contain bioactive/nutraceutical lipids and proteins, is a valuable byproduct of the process.     

Synthesis and characterization of a potential prebiotic trisaccharide from cheese whey permeate and sucrose by Leuconostoc mesenteroides dextransucrase

The production of new bioactive oligosaccharides is currently garnering much attention for their potential use as functional ingredients. This work addresses the enzymatic synthesis and NMR structural characterization of 2-α-D-glucopyranosyl-lactose derived from sucrose:lactose and sucrose:cheese whey permeate mixtures by using a Leuconostoc mesenteroides B-512F dextransucrase. The effect of synthesis conditions, including concentration of substrates, molar ratio of donor/acceptor, enzyme concentration, reaction time, and temperature, on the formation of transfer products is evaluated. Results indicated that cheese whey permeate is a suitable material for the synthesis of 2-α-D-glucopyranosyl-lactose, giving rise to yields around 50% (in weight respect to the initial amount of lactose) under the optimum reaction conditions. According to its structure, this trisaccharide is an excellent candidate for a new prebiotic ingredient, due to the reported high resistance of α-(1→2) linkages to the digestive enzymes in humans and animals, as well as to its potential selective stimulation of beneficial bacteria in the large intestine mainly attributed to the two linked glucose units located at the reducing end that reflects the disaccharide kojibiose (2-α-D-glucopyranosyl-D-glucose). These findings could contribute to broadening the use of important agricultural raw materials, such as sucrose or cheese whey permeates, as renewable substrates for enzymatic synthesis of oligosaccharides of nutritional interest.     

Relationship between MALDI-TOF analysis of beta-CN f193-209 concentration and sensory evaluation of bitterness intensity of aged cheddar cheese

An internal standard method was previously developed to measure the concentration of a synthetic bitter peptide, beta-CN f193-209, by matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry. The objective of this study was to evaluate the relationship between beta-CN f193-209 concentration in an aqueous extract of aged Cheddar cheese and bitterness intensity of the cheese. Concentrations of beta-CN f193-209 in cheese extracts were determined by MALDI-TOF at 0, 120, 180, and 270 days. Trained panels evaluated the bitterness intensity of the cheeses at 180 and 270 days. Correlation coefficients between MALDI and sensory data at 180 and 270 days were 0.803 and 0.554, respectively. The decreased correlation may be due to the presence of other bitter peptides more responsible for bitterness at longer aging or the production of compounds that mask bitterness intensity.     

Modified atmosphere packaged cheddar cheese shreds: influence of fluorescent light exposure and gas type on color and production of volatile compounds

The influences of fluorescent light exposure and packaging atmosphere on the headspace volatiles and color of Cheddar cheese shreds were evaluated using gas chromatography-mass spectrometry and spectrocolorimetry, respectively. Cheddar cheeses were packaged under atmospheres of 100% carbon dioxide or 100% nitrogen and stored at 4 degrees C under fluorescent light for 6 weeks. Cheeses stored under carbon dioxide contained higher concentrations of aldehydes and fatty acids and lower concentrations of alcohols and esters than cheeses stored under nitrogen. Carbon dioxide atmospheres potentiated light-induced oxidation in shredded Cheddar cheeses, as evidenced by aldehyde and fatty acid headspace volatiles measured following storage. Color bleaching occurred only in cheeses packaged under carbon dioxide and exposed to light. The shift in color is proposed to be due to an interaction between carbon dioxide and high-intensity light, leading to the oxidation of the pigment molecule, bixin. The results have significant implications for procedures used to handle and store pigmented cheeses to ensure desirable flavor and consumer acceptability.     

Heat-induced aggregation of whey proteins: comparison of cheese WPC with acid WPC and relevance of mineral composition

Heat-induced aggregation of whey proteins in solutions made from two commercial whey protein concentrates (WPCs), one derived from mineral acid whey (acid WPC) and the other from cheese whey (cheese WPC), was studied using polyacrylamide gel electrophoresis (PAGE), size exclusion chromatography (SEC), and transmission electron microscopy (TEM). Heat treatment (75 degrees C) of acid WPC solutions (12.0%, w/w, pH 6.9) resulted in formation of relatively small "soluble" aggregates that were predominantly disulfide-linked. By contrast, heat treatment of the cheese WPC solutions (under the same conditions) caused formation of relatively large aggregates, containing high proportions of aggregates linked by noncovalent associations. The rate of aggregation of both beta-lactoglobulin and alpha-lactalbumin at 75 degrees C, measured as the loss of native proteins by PAGE, was higher in the cheese WPC solution than in the acid WPC solution. Cross dialysis of the two WPC solutions resulted in alteration of the mineral composition of each WPC solution and reversing their heat-induced aggregation behavior. The results demonstrated that the mineral composition is very important in controlling the aggregation behavior of WPC products.     

纳滤技术对干酪乳清脱盐性能的影响

为了开发经济可行的乳清脱盐技术,提高乳清产品品质及其附加值,该研究采用截留液全循环连续错流纳滤操作装置对干酪甜乳清进行纳滤脱盐处理。考察了不补水纳滤浓缩及不同补水透析方式对乳清脱盐率的影响,以脱盐率为指标进行工艺优化,选取适宜的脱盐操作工艺。结果表明,在1.1 MPa的操作压力下,控制溶液温度为30℃,系统流量为4.5 L/min,纳滤至体积浓缩比（VCR）为1.5时,以渗透速率向截留液中补充等同于浓缩液体积的去离子水,在相同的纳滤时间内,脱盐效果较好。纳滤乳清经喷雾干燥后,相对原料乳清粉脱除了45%的盐分,乳清蛋白和乳糖基本完全截流。     

积盐条件下土壤酸化过程的特异性研究

为探求设施内土壤积盐酸化与露地酸化的区别,人为模拟酸化和盐基淋失(自然洗盐)过程,分析洗盐前后土壤酸度特征的变化。结果表明:洗盐使电导值、有效钙(A-Ca)、交换性酸(EA)、有效阳离子交换量(CEC)、活性锰(Ac-Mn)含量均显著降低,活性铁铝(Ac-Fe、Ac-Al)含量、盐基饱和度(BSP)保持稳定或显著增高,p H显著升高。洗盐前后,土壤的EA、Ac-Al和Ac-Fe均随着p H的降低显著增高,而Ac-Mn、CEC均随着p H的降低显著下降;在出现一定量EA以后,BSP随p H降低显著下降,表明积盐酸化与露地酸化本质相同。但在等量酸加入时,设施内积盐土壤耕层酸化更快,酸害更严重,且易积盐,在治理酸化时须避免引入更多的盐分,以防加重盐害。     

Impact of whey pH at drainage on the physicochemical, sensory, and functional properties of mozzarella cheese made from buffalo milk

In this study, the effects of whey pH at drainage on the physicochemical, sensory, and functional properties of mozzarella cheese made from buffalo milk during storage were investigated. Four cheese samples were manufactured using starter culture at different whey pH values [(A) 6.2, (B) 5.9, (C) 5.6, and (D) 5.3] and analyzed on the 1st, 28th, and 56th day. Ash, calcium, and phosphorus concentrations decreased as the whey pH at drainage was lowered. Cheese yield and calcium recovery were the highest in D cheeses. During storage, expressible serum levels decreased and nonexpressible serum levels increased, indicating an increase in the water holding capacity of the cheeses. Reducing the calcium content of cheeses increased meltability values, but an overly low calcium level (D cheeses) had an adverse effect on the meltability. The melting properties of cheese samples, except D cheeses, were improved with aging. A cheeses were the hardest and D cheeses the softest throughout storage. The 1st day sensory evaluations revealed that C and D cheeses were preferred and that A cheeses were not. All sensory properties of A cheeses were improved with storage. D cheeses were rated inferior to the others at the end of the storage time.     

Soil acidification by atmospheric pollution and forest growth

In recent years concern has been expressed about the danger of harmful pollution deposits which affect areas at great distances from the emission sources. The investigation was so designed that a possible reaction in growth resulting from a supposed acidification could be observed as far as possible. A poorer growth development was observed in regions, which are suspected of being more susceptible to acidification than those regions which are presumed to be less susceptible in this respect. We have found no good reason for attributing the reduction in growth to any cause other than acidification.     

Removal of cholesterol from Cheddar cheese by beta-cyclodextrin

This study was carried out to determine the cholesterol removal rate and resulting changes in flavor, fatty acid and bitter amino acid production in reduced-cholesterol Cheddar cheese, made by cream separation followed by 10% beta-cyclodextrin (beta-CD) treatment. The cholesterol removal from the cheese was 92.1%. The production of short-chain free fatty acids (FFAs) increased the ripening time in control and cream-treated cheeses. The quantity of short-chain FFAs released between treatments during ripening was different, while not much difference was found in the production of neutral volatile compounds in the samples. Reduced-cholesterol cheese produced much higher levels of bitter amino acids than the control. In sensory analysis, the texture score of control Cheddar cheese increased significantly with ripening time; however, that of the cream treatment group decreased dramatically with ripening time. On the basis of our results, we conclude that the cheese made from beta-CD-treated cream had a higher rate of cholesterol removal and ripened rapidly.     

羊奶乳清蛋白水解物的酶解制备

采用Alcalase与Flavourzyme两种酶对羊奶乳清蛋白进行水解,以水解度为指标,对两种酶单独使用及复合使用水解羊奶乳清蛋白的工艺条件进行了研究。试验结果显示:采用Alcalase与Flavourzyme复合水解羊奶乳清蛋白的效果较好,特别是采用先添加Flavourzyme后加入Alcalase进行水解,不仅能提高羊奶乳清蛋白的水解度,使其达到32.81%,而且对改善水解液的口感有较大的作用。     

Protein-peptide interactions in mixtures of whey peptides and whey proteins

The effects of several conditions on the amounts and compositions of aggregates formed in mixtures of whey protein hydrolysate, made with Bacillus licheniformis protease, and whey protein isolate were investigated using response surface methodology. Next, the peptides present in the aggregates were separated from the intact protein and identified with liquid chromatography-mass spectrometry. Increasing both temperature and ionic strength increased the amounts of both intact protein and peptides in the aggregates. There was an optimal amount of added intact WPI that could aggregate with peptides, yielding a maximal amount of aggregated material in which the peptide/protein molar ratio was around 6. Under all conditions applied, the same peptides were observed in the protein-peptide aggregates formed. The dominant peptides were beta-lg AB [f1-45], beta-lg AB [f90-108], and alpha-la [f50-113]. It was hypothesized that peptides could form a kind of glue network that can include beta-lactoglobulin via hydrophobic interactions at the hydrophobic binding sites at the surface of the protein.     

Evidence for acidification of sensitive Scottish soils by atmospheric deposition

The Scottish soils most sensitive to acidification from acid deposition are peats and those derived from quartzite or Devonian and Torridonian sandstones. It is shown that the surface horizons of Calluna moorland podzols derived from these mineral parent materials behave in a similar way to peats, in that their pH depends upon cation exchange equilibria between H⁺ and Ca²⁺. The pH is therefore related, as might be expected from the ratio law, to the ratio [H⁺]:[Ca²⁺], and this relationship may be used to predict the effect of emission reductions or increases upon these soils.     

Enzymatic cleaning of inorganic ultrafiltration membranes fouled by whey proteins

The aim of this work was to study the cleaning of inorganic membranes fouled with whey protein solutions using the enzymatic formulation Alcalase (Novo Nordisk A/S). Hydraulic and chemical methods were considered to characterize the cleanliness of the membranes. Cleaning efficiency was observed to be a function of the operating conditions. The operating conditions tested were the following: recycling versus non-recycling of permeate, pH of the cleaning solution, addition of alkali to regulate the pH, enzymatic agent concentration, and cleaning time. The best conditions to perform the cleaning were related to the best conditions to hydrolyze whey proteins in a discontinuous reactor using the same enzyme preparations. Very high cleaning efficiencies (>90%) were achieved in short operating times (20 min). However, residual matter was observed on the membrane surface.     

Effect of lake acidification on the adsorption of phosphorus by sediments

The retention properties of acidic and non-acidic lake sediments were determined in order to assess the effects of lake acidification on the immobilization of P from solution by sediments. The adsorption of P by solids was described by the Langmuir model which was used to determine the sorption parameters, e.g. sorption maxima and equilibrium constant of adsorption. The pH of solution and the chemical and mineralogical characteristics of sediments affect mainly the magnitude of adsorption maxima. The binding strength of the adsorbed complex is similar for all the investigated sediments (Δ=?25.3 to ?28.5 kJ mol^?1) and it is affected little by variation in pH or by chemical and mineralogical composition of sediments. The results indicate that the magnitude of P removal is determined more by sediment chemistry and mineralogy (amorphous Al/Fe oxy-hydroxides, carbonate content) than by pH of the water.