Influence of microfiltration and adjunct culture on quality of Domiati cheese.

The effects of microfiltration and pasteurization processes on proteolysis, lipolysis, and flavor development in Domiati cheese during 2 mo of pickling were studied. Cultures of starter lactic acid bacteria isolated from Egyptian dairy products were evaluated in experimental Domiati cheese for flavor development capabilities. In the first trial, raw skim milk was microfiltered and then the protein:fat ratio was standardized using pasteurized cream. Pasteurized milk with same protein:fat ratio was also used in the second trial. The chemical composition of cheeses seemed to be affected by milk treatment-microfiltration or pasteurization-rather than by the culture types. The moisture content was higher and the pH was lower in pasteurized milk cheeses than in microfiltered milk cheeses at d 1 of manufacture. Chemical composition of experimental cheeses was within the legal limits for Domiati cheese in Egypt. Proteolysis and lipolysis during cheese pickling were lower in microfiltered milk cheeses compared with pasteurized milk cheeses. Highly significant variations in free amino acids, free fatty acids, and sensory evaluation were found among the cultures used in Domiati cheesemaking. The cheese made using adjunct culture containing Lactobacillus delbrueckii ssp. lactis, Lactobacillus paracasei ssp. paracasei, Lactobacillus casei, Lactobacillus plantarum, and Enterococcus faecium received high scores in flavor acceptability. Cheeses made from microfiltered milk received a higher score in body and texture compared with cheeses made from pasteurized milk.

The cell-bound proteinase system of Lactobacillus casei--purification and characterization.

The cell-wall crude extract from Lactobacillus casei NCDO 151 was partially purified by DEAE-Sephacel chromatography. Three active fractions were eluted. Two major peaks (eluted with 0.05 M and 0.27 M phosphate buffer) were further investigated. Peak I represented enzymatic activity with an optimum temperature of 40 degrees C, an optimum pH of 7.0 and was strongly inhibited by the serine proteinase inhibitor phenylmethylsulfonylfluoride. Peak II represented an enzymatic activity with an optimum temperature of 45 degrees C, an optimum pH of 7.5 and was totally inhibited by p-hydroxymercuribenzoate. None of the enzymes was affected by the metal chelator ethylenediaminetetraacetic acid at a concentration up to 1 x 10(-2).

Purification of X-prolyl dipeptidyl aminopeptidase from Lactobacillus casei subspecies.

Prolyl dipeptidylaminopeptidases from two subspecies of Lactobacillus casei were purified and biochemically characterized. L. casei ssp. casei UL21 (a debittering strain) and L. casei ssp. rhamnosus UL26 (a non-debittering strain) were the source bacteria for this study. Purification of the enzymes from both the sources was effected by a gel filtration step through Sephacryl S-300 followed by ion-exchange chromatography through DEAE Sephacel. This rendered an electrophoretically homogeneous enzyme preparation. The purified enzymes from both the sources showed similar temperature optimum (45 degrees C) and pH optimum (7.0). Their activity profiles on various substrates and the nature of inhibition by different inhibitors were also found to be similar, indicating that this enzyme is perhaps not significantly involved in the debittering process during the maturation of cheese.

[Peptide hydrolases of lactobacilli of the Thermobacterium group. I. Demonstration of these activities in Lactobacillus helveticus, L. acidophilus, L. lactis and L. bulgaricus]. / Les peptide-hydrolases des lactobacilles du groupe Thermobacterium. I. Mise en évidence de ces activités chez Lactobacillus helveticus, L. acidophilus, L. lactis et L. bulgaricus.

The intracellular peptide hydrolase activities of Lactobacillus helveticus, L. acidophilus, L. lactis, and L. bulgaricus were determined using various aminopeptidase, dipeptidase, and carboxypeptidase substrates in addition to casein and whey protein fractions. The different activities were then separated using disc gel electrophoresis. Each bacterium had aminopeptidase activity towards various amino acid beta-naphthylamides and dipeptides. The four species also showed bands of true dipeptidase activities on a large number of dipeptides. Intracellular enzymes from thermophilic lactobacilli also hydrolysed the whey proteins (alpha-lactalbumin and beta-lactoglobulin). From the results of electrophoresis on beta-casein and alpha s1-casein it was shown that beta-casein was totally hydrolysed by L. lactis while it was only partially hydrolysed by the intracellular enzymes of L. acidophilus and L. bulgaricus. On the other hand, alpha s1-casein was only partially hydrolysed by L. helveticus, L. lactis, and L. bulgaricus.

Microencapsulated enzyme systems for the acceleration of cheese ripening.

Enzymes and substrates encapsulated in either milkfat-coated microcapsules or liposomes have been investigated for potential use as agents to accelerate cheese ripening. Milkfat-coated microcapsules have been used to efficiently encapsulate cell-free extracts, viable cells, purified enzymes, and spores. Encapsulation efficiency was dependent on the conditions used during capsule production. Addition of these microcapsules to cheese has resulted in increased levels of flavour compounds such as diacetyl, acetoin, methanethiol, and methyl ketones, compared to levels in control cheeses. Limitations due to cofactors have been overcome by co-encapsulating enzymes which recycle needed cofactors. Liposomes have been used to carry cell-free extracts and enzymes into cheese. Trials with different types of liposomes revealed that enzymes could be entrapped more efficiently and liposomes retained in the cheese curd better when multilammelar vesicles rather than small unilamellar vesicles or reverse phase evaporation vesicles were used. The stability of liposome preparations was found to be adversely affected by increased pH, temperature, and sodium chloride concentrations, as well as by negative surface charge. Encapsulation efficiency was found to increase by using a dehydration-rehydration procedure for liposome preparation. Temperature sensitive liposomes were investigates as a means of obtaining controlled release of the enzymes into the cheese.

Ripening of cheddar cheese with added attenuated adjunct cultures of lactobacilli.

We made Milled curd Cheddar cheese with Lactococcus starter and an adjunct culture of Lactobacillus helveticus I or Lactobacillus casei T subjected to different attenuation treatments: freeze shocking (FS), heat shocking (HS), or spray drying (SD). Proteolysis during cheese ripening (0 to 6 mo), measured by urea-PAGE and water-soluble nitrogen, indicated only minor differences between control and most adjunct-treated cheeses. However, there were significant differences in the effect of Lactobacillus adjuncts on the level of free amino nitrogen in cheese. Cheeses made with FS or HS Lb. helveticus adjunct exhibited significantly greatest rates of free amino group formation. Lipolysis as measured by total free fatty acids was consistently highest in adjunct-treated cheeses, and FS Lb. casei-treated cheeses showed the highest rate of free fatty acid formation followed by FS Lb. helveticus treated cheeses. Mean flavor and aroma scores were significantly higher for cheeses made with Lb. helveticus strain. Freeze-shocked Lb. helveticus-treated cheeses obtained the highest flavor and aroma scores. Sensory evaluation indicated that most of the adjunct-treated cheeses promoted better texture and body quality.

The Peptide Hydrolase System of the Leuconostoc.

The intracellular peptide hydrolase activities of Leuconostoc species were determined using various aminopeptidase, dipeptidase, carboxypeptidase substrates, and casein. The activities were separated by disc gel electrophoresis. All strains had aminopeptidase activity as determined with amino acid ß-napthylamides and dipeptidase. All strains also showed bands or true dipeptidase activities on a large number of dipeptidase.

Adjunct cultures: recent developments and potential significance to the cheese industry.

Several previous reviews have described different ways to enhance the flavor and texture of cheese, including use of live cells and nonviable attenuated cells as adjunct cultures. However, comparisons between viable and nonviable cultures were never discussed in these reviews. In addition, recent publications on adjunct cultures have not been covered in previous reviews. This article will survey the more recent work on adjunct cultures--with particular attention to whether the adjuncts contained viable or nonviable cells--and propose areas where additional research is needed.

Peptide hydrolases of Lactobacillus casei: isolation and general properties of various peptidase activities.

Discovery of an endopeptidase by gel chromatography and separation of 3 exopeptidases (a dipeptidase, an aminopeptidase and a specific carboxypeptidase) from Lactobacillus casei NCDO 151 by affinity chromatography is described. The 3 exopeptidases were strongly inhibited by the metal chelators EDTA and 1,10-phenanthroline but were reactivated with Co2+ and Mn2+. The pH optima for aminopeptidase, dipeptidase and carboxypeptidase activities were 6.5, 7.6 and 7.2, respectively. Maximum activity was obtained at 45 degrees C for the aminopeptidase, at 30 degrees C for the dipeptidase and at 40 degrees C for the carboxypeptidase. The substrate specificities of the 3 enzymes were also studied. The properties of these 3 enzymes are compared with those of other bacteria.

Cell-Wall-Associated Proteinases in Lactobacillus casei and Lactobacillus plantarum.

Information concerning cell-wall associated proteinases of lactobacilli is limited. In Lactobacillus casei and Lactobacillus plantarum , presence of such proteinase is clearly shown. Differences between several strains were noticed. Higher cell-wall-associated proteinase activity can be measured in extracts obtained from milk-grown cells when compared to MRS-grown cells. No aminopeptidase, dipeptidase or carboxypeptidase activities were detected in the cell-wall-associated proteinase fraction. Isoelectric focusing of αs1-casein hydrolysates obtained by the action of this fraction from L. casei grown in milk revealed the presence of a major hydrolysis product and three minor degradation products with isoelectric points more acidic than αS1. Beta-casein was also degraded by the cell-wall extract with formation of one major product and several minor products with isoelectric points more acidic than ß-casein. Two major hydrolysis products with isoelectric points higher than ß-casein were also detected. Isoelectric focusing of αs1- and ß-casein hydrolysates obtained by the action of the intracellular extracts of L. casei grown either in milk or in MRS broth shown identical patterns. As with L. casei , two strains of L. plantarum exhibited cell-wall proteinase activity. Milk-grown cells were more proteolytic than MRS-grown cells. Generally L. plantarum was significantly less proteolytic than L. casei .