Manufacture Of Yogurt Research Articles

Production of thermophilic lactic acid starters in mixed cultures

Thermophilic lactic acid starters, Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus, were produced by controlled mixed cultures. The total bacterial concentration and the population ratio at the end of fermentation were fixed by the operating conditions (pH and temperature) and by the initial percentage of S. thermophilus in the inoculum. The suitability of these mixed starters for yoghurt manufacture was determined from their aci- dification activity. This was not significantly different from that obtained with equivalent mixing of pure cultures. During preservation, the rnixed starters were slightly less resistant, both in fro- zen and freeze-dried forms, than starters obtained from pure cultures. The productivity of the mixed cultures was twice from that obtained with the traditional starter production process, whatever the final population ratio. Finally, the ability to control the mixed starter eultures, the increased pro- ductivity and their properties (acidification and preservation) proved their interest for industrial applications. © InralElsevier, Paris.

Manufacture and Quality of Iron-Fortified Yogurt

Yogurts (nonfat and low fat) were manufactured and fortified with 10, 20, and 40mg of iron/kg of yogurt. Growth of starter culture bacteria and non-starter culture bacteria as well as lipid oxidation of the yogurts were monitored over 30 d of storage at 4°C. Sensory characteristics of the yogurts were determined during that time by a trained panel of judges, and consumer panels were used to test acceptability of iron-fortified yogurt.Counts of Lactobacillus delbrueckii ssp. bulgaricus and Streptococcus thermophilus after 1 d of storage in iron-fortified skim yogurts were 7.0 x 108 cfu/ml, which were not significantly different from numbers in unfortified yogurts. Counts decreased to 2.5 x 108 and 1.9 x 108 cfu/ml for L. delbrueckii ssp. bulgaricus and S. thermophilus, respectively, after 30 d of storage. Fortifying yogurt with iron did not support the growth of Pseudomonas flurescens or Escherichia coli.No significant increases in chemical oxidation, as measured using the thiobarbituric acid assay, were detected as a consequence of iron fortification. Trained panelists scored all yogurts for oxidized, metallic, bitter, and other off-flavors in the range of “not perceptible” to “very slightly perceptible”. Iron-fortified yogurts had slightly higher oxidized flavor scores than did the control yogurt. There was no increase in metallic, bitter, or other off-flavors. The consumer panel did not detect any significant differences in the appearance, mouthfeel, flavor, or overall quality between fortified and unfortified flavored yogurts. All yogurt samples were liked by the consumer panelists, suggesting that yogurt is a suitable vehicle for iron fortification.

Continuous yoghurt manufacture

Continuous yoghurt manufacture

Comparison of .BETA.-Lactoglobulin Content in Dairy Products by Inhibition ELISA and Immunoblotting.

To estimate the effect of food processing on allergen content in dairy products, β-lactoglobulin (β-LG) contents of 4 milks, 5 yogurts and 6 cheeses were compared using inhibition ELISA (enzyme-linked immunosorbent assay), SDS-PAGE and immunoblotting. Results of the inhibition ELISA suggested that low temperature-pasteurized milk contained several times higher levels of β-LG than high temperature-pasteurized milk, and that yogurts contain a lower amount of β-LG than milks. On the contrary, results of SDS-PAGE and immunoblotting suggested that the degradation of milk proteins including β-LG during yogurt manufacturing was not very extensive. These results suggest that yogurts contain factor(s) which interfere some reactions of inhibition ELISA. β-LG was also detected in cheeses, though the level was lower than that of milks. Though milk proteins were degraded most extensively in Roquefort cheese, its β-LG level was the highest. Among them, processed cheese had the lowest amount of β-LG, followed by Emmental cheese. These results suggest that an appropriate application of specific bacteria is useful for the preparation of low allergenic dairy products.

Viability of yoghurt and probiotic bacteria in yoghurts made from commercial starter cultures

Viability of yoghurt and probiotic bacteria was assessed during manufacture and 35 d storage in yoghurt made from four commercial starter cultures. The titratable acidity, pH and dissolved oxygen content showed similar patterns of increase or decrease during manufacture and storage of yoghurt, whereas concentration of hydrogen peroxide increased in the product prepared with cultures that contained L. delbrueckii ssp. bulgaricus. The increase in numbers of probiotic organisms during manufacture and the viability of these organisms during storage were dependent on the species and strain of associative yoghurt organisms. The viability of L. acidophilus was affected by the presence of L. delbrueckii ssp. bulgaricus, whereas bifidobacteria exhibited better stability in the yoghurt prepared from cultures that contained L. delbrueckii ssp. bulgaricus. The viability of both probiotic organisms was improved when the dissolved oxygen concentration was low in the product. The storage temperature of yoghurt affected the viability of bifidobacteria, but not L. acidophilus. The variations in titratable acidity, pH, dissolved oxygen and hydrogen peroxide were almost identical at storage temperatures of 4 and 10 °C. In one of the commercial cultures, 3 log cycles inhibition of bifidobacteria was observed from initial counts of >106 mL−1.

The manufacture of set-type natural yoghurt containing different oils — 1. Compositional quality, microbiological evaluation and sensory properties

Yoghurts rich in poly- and mono-unsaturated fatty acids were manufactured from reconstituted skimmed milk powder using vegetable oils (olive, groundnut, sunflower or maize) to replace the milk fat. They were compared with a yoghurt containing anhydrous milk fat [AMF, 1.5% (ww)]. The vegetable oil-based yoghurts [at a 1.5% (ww) level of addition] were different from the control yoghurt containing AMF. The microbiological quality of all the yoghurts was excellent, and the yoghurt starter organisms were in abundance. The sensory panel identified significant differences (P < 0.05) between products containing AMF and vegetable oils in terms of whey separation and some flavour and aroma attributes (acidic, oxidised, unclean and after-taste). Copyright

The manufacture of set-type natural yoghurt containing different oils — 2: Rheological properties and microstructure

Abstract Yoghurts rich in poly- and mono-unsaturated fatty acids were manufactured from reconstituted skimmed milk powder using vegetable oils (olive, groundnut, sunflower or maize) to replace the milk fat. They were compared with a yoghurt-containing anhydrous milk fat [AMF, 1.5% ( w w )]. The vegetable oil-based yoghurts [at a 1.5% ( w w ) level of addition] were different from the control yoghurt containing AMF. Whey separation was higher and firmness was lower for all vegetable oil-containing yoghurts than for the product containing AMF. Scanning electron microscopy revealed similar microstructure, including the distribution of void spaces filled with milk serum (porosity of the protein matrices), whereas transmission electron microscopy showed the interaction of the vegetable oil droplets with casein micelles and their participation in the formation of the gel matrices.

Enumeration of starter cultures in fermented milks

SummarySome media available for the isolation and enumeration of starter cultures employed for the manufacture of cheese, yogurt and bio-yogurt were examined. Reddy's medium or a modification of Elliker's medium was found to be most satisfactory forLactococcusspp., while trypticase phytone yeast (TPY) agar with a mixture of antibiotics proved suitable for the discrete enumeration ofBifidobacteriumspp. The inclusion of Prussian blue (PB) in reinforced clostridial medium or tryptone proteose peptone yeast extract (TPPY) agar gave excellent differential counts for the starter bacteria in yogurt even when the culture was imbalanced, while TPPY (PB) agar allowed the visible separation of all four of the organisms that might be found in a typical bio-yogurt, namelyLactobacillus delbrueckiisubsp.bulgaricus, Streptococcus thermophilus, a,Bifidobacteriumsp. andLb. acidophilus. It was noted that variation among different strains of any given species could change the expected reactions, so for quality control purposes the suggested media may need to be modified to cope with the specific cultures in use.

Probiotic frozen yogurt containing high protein and calcium (1996)

A new frozen yogurt manufacturing procedure that is easily adaptable to the current practices of the frozen yogurt industry has been developed with probiotic culture and ultrafiltrated milk. The ultrafiltrated milk was heated to 185 degrees F for 35 min to obtain a desirable gel structure when fermented with the traditional yogurt culture of Streptococcus thermophilus and Lactobacillus bulgaricus. Probiotic cultures (Bifidobacterium and Lactobacillus spp.) were added to the yogurt mix just before freezing. The yogurt mix was frozen to an 85% overrun and hardened at -20 degrees F. The frozen product contained viable culture organisms at greater than or equal to 107 cells per gram and was stable for 6 mo. The frozen yogurt also contained twice the amount of protein, three times as much calcium, and nearly one-third less lactose than similar commercial products. The new product had excellent flavor, body, texture, and overall quality.; Dairy Day, 1996, Kansas State University, Manhattan, KS, 1996

Stability of the intense sweetener neohesperidine DC during yogurt manufacture and storage

The stability of the intense sweetener neohesperidine dihydrochalcone (DC) has been assessed during yogurt manufacture and storage. No significant decomposition was detected during and after milk pasteurization, the fermentation process and storage for 6 weeks at 3 °C. In addition, the maximum authorized concentration of neohesperidine DC did not affect the rate of acidification by lactic acid bacteria during the fermentation process. Taken together, these results suggest that neohesperidine DC can be added to milk products and will remain stable throughout pasteurization and fermentation processes.

Different inhibition of Lactobacillus delbrueckii subsp. bulgaricus by D‐ and L‐lactic acid: effects on lag phase, growth rate and cell yield

Inhibition of Lactobacillus bulgaricus by lactic acids at constant pH is governed by two factors: the total concentration of lactic acids and the D/L ratio of lactic acid stereoisomers. L‐Lactic acid is more inhibitory than the D‐isomer, the latter being the only isomer produced by Lact. bulgaricus. The major inhibitory effect is an extremely prolonged lag phase (2–39 h for the range 0–25 g 1‐1 added lactic acids). Added lactic acids reduce the maximum cell concentration obtained in pH controlled fermentations, but have virtually no effect on maximum specific growth rate and on the yield of biomass on produced lactic acid. The added lactic acids have no effect on the growth‐related ATP consumption nor on the non‐growth related ATP consumption. The culture is heterogeneous since a part of the culture is unable to grow in the presence of L‐lactic acid. A different inhibitory effect of D‐ and L‐lactic acid has implications for yoghurt manufacture and potential for improved food preservation.

Stability of aflatoxin M1 during manufacture and storage of yoghurt, yoghurt‐cheese and acidified milk

AbstractYoghurt, yoghurt‐cheese and acidified milk were prepared from pasteurised half‐cream milk, naturally contaminated with aflatoxin M1 (AFM1) and then were stored at 4°C for 2 weeks. Levels of AFM1 in these dairy products were high, and then began to decrease during storage period at 4°C. Most of the AFM1 (recoveries of 71%) appeared in yoghurt‐cheese after 14 days, this is due to AFM1 being associated with casein fraction. Whereas pH values of yoghurt‐cheese during refrigerator storage ranged from 5.15 to 4.65 and titratable acidity ranged from 3.9 to 3.5 g lactic acid litre−1, whilst AFM, (recoveries of 41%) from yoghurt after manufacture and storage was much more susceptible to reduction by storage this is due to the higher acidity (range 2.3–3.1 g litre−1) of yoghurt by the action of microorganisms, besides the changes in pH values (5.10–4.70). When acidified milk was used the recoveries of toxin were 34.2% after 2 weeks; pH values ranged from 2.95 to 2.85 and titratable acidity ranged from 2.3 to 2.2 g litre−1 during storage.

Metabolic interaction between Streptococcus thermophilus and Lactobacillus bulgaricus in single and mixed starter yoghurts

AbstractYoghurt was manufactured with mixed starter of S. thermophilus and L. bulgaricus or a single starter of either in the presence or absence of 600 ppm free amino acids mixture (glutamic acid, histidine, cysteine, valine, methionine and tyrosine) and/or 600 ppm of sodium formate. Results showed that the acidity, total volatile fatty acids (TVFA), NPN, total free amino acids and soluble tyrosine contents of different yoghurt samples increased gradually during storage at 5–8 °C for 7 days especially in the mixed starter yoghurt fortified with free amino acids mixture and Na formate. Organoleptic evaluation showed that the flavour of single strain starter yoghurt with free amino acids mixture of Na formate gave nearly the flavour of control yoghurt samples. However, the mixed starter yoghurt fortified with free amino acids mixture and Na formate gave more acceptable flavour. It could be concluded that addition of free amino acids mixture and/or Na formate to yoghurt stimulated the activity of starter bacteria. Also manufacture of yoghurt using a single starter of S. thermophilus or L. bulgaricus should be associated with addition of free amino acids mixture or Na formate to yoghurt milk respectively.

Production of a yogurt‐like product from plant foodstuffs and whey. Substrate preparation and fermentation

AbstractA mixed substrate composed of soya milk, oat flour and dried cheese whey (82, 11 and 7% respectively) had a content of lactose and protein similar to that of milk used for yogurt manufacture. Heat treatment for 20 min at 80°C resulted in a viscosity similar to that of yogurt whilst removing coliform and mesophilic aerobic bacteria, moulds and yeasts. Fermentation with traditional yogurt bacteria did not increase viscosity further, and the final product had similar acidity and texture to yogurt. Acid development, carbohydrate consumption, proteolysis and starters counts were followed during fermentation. The fermentation profile of the mixed substrate was very similar to that of milk.

Preparation of whey protein concentrate from salted whey and its use in yogurt

SummarySalted whey (7–8% NaCl) was concentrated by ultrafiltration by a factor of 20. Sweet whey equal to the retentate volume was added and ultrafiltration was continued to a concentration factor of 20. Addition of sweet whey and ultrafiltration was repeated twice more for almost complete removal of salt from whey protein concentrate (WPC). The protein content of WPC was adjusted to 3·5% using sweet whey and the mixture was heated to 65°C for 30 min. This was mixed with buffalo milk at the rate of 0, 10, 20 or 30% and then heated at 80°C for 1, 5 or 20 min before use for yogurt manufacture. The chemical, rheological and organoleptic properties of the yogurt were investigated. WPC could be added to buffalo milk at up to 20% without affecting the quality of the yogurt produced. On the contrary, it improved the texture, mouthfeel and wheying-off of yogurt from buffalo milk. Yogurt with 30% WPC had an unacceptably weak body and texture for a set product. Heating at 80°C for 5 min was sufficient to produce good quality yogurt from buffalo milk containing WPC.

Effect of Sundae-Style Yogurt Fermentation on the Aspartame Stability in Fruit Preparation

We assessed the stability of aspartame during fermentation of milk to manufacture yogurt with fruit on the bottom (sundae-style yogurt) using different direct-set cultures and incubation temperatures. Aspartame recovery based on original amount was determined using HPLC. Aspartame recovery was 95 or 90% in yogurts produced using a 6-h incubation at 43.3°C and 13h at 32.2°C, respectively. Aspartame, therefore, has excellent stability in fruit preparation during the manufacture of sundae-style yogurt.

Physical Properties of Yogurt Made from Milk Treated with Proteolytic Enzymes

Milk used in the manufacture of yogurt is often subjected to storage times and temperatures that permit protein degradation catalyzed by bacterial or native proteases. The objective of this research was to evaluate the effects of proteolysis of milk on the physical properties of yogurt. Milk was treated with either crude extracts of bacterial protease or purified plasmin. Treated milk was immediately made into yogurt, which was stored at 7°C and analyzed after 1, 8, and 15 d. Yogurt made from milk pretreated with microbial protease had higher firmness, syneresis, and apparent viscosity than the untreated product. Yogurt made from milk treated with plasmin had significantly lower firmness and apparent viscosity, and after 8 d, lower syneresis as compared with the control. Yogurt made from milk treated with either protease had lower water-holding capacity and protein hydration than untreated controls. Proteolysis of milk did not produce consistent effects on yogurt culture levels, although fermentation was more rapid in the treated milks. Results indicate that proteolysis of milk results in yogurt of substantially different physical properties and that the effects of proteases from psychrotrophic bacteria on the properties of yogurt differ from the effects of plasmin.

Comparison of Milk‐Based and Soymilk‐Based Yogurt

The study was conducted to investigate the efficacy of the activated carbon treatment for improving the flavor of soymilk-based yogurt products and to determine the functionality of nonfat dry milk and whey protein concentrate in the manufacture of milk-based and soymilk-based yogurt. These products were subjected to a chemical analysis and characterized for physical and sensory properties

Monitoring of B-complex vitamins in yogurt during fermentation

SummaryEight commercially available yogurt starter cultures were examined for their ability to synthesize water-soluble vitamins. In order to yield comparable assaying conditions, 12·5% reconstituted whole milk was used for yogurt production throughout the experiments. When applying the traditional method of yogurt manufacture (short-time incubating at 42 °C/3–4 h) with all cultures the following vitamins were enriched during fermentation by more than 20%: thiamin (two cultures), pyridoxine (four cultures), folic acid (one culture), and biotin (two cultures). Two starter cultures were selected and used to compare vitamin profiles during the two different methods of fermentation. In contrast to short-time incubation, long-time yogurt production (30 °C/14–16 h) led to a lesser production of folic acid, but to increased concentrations of thiamin and of nicotinic acid.

Effects of β-lactoglobulin and κ-casein genetic variants and concentrations on syneresis of gels from renneted heated milk

Milk protein genetic polymorphism has a major influence on the composition of milk, and on its processing properties, including yield of cheese (see Schaaret al.1985; McLeanet al.1984, 1987; McLean, 1987). However, there appears to be little information on the effects of milk protein genetic variants on syneresis of cheese curd. The effect of casein composition on syneresis was studied by Pearseet al.(1986), who found that syneresis was affected only by the level of β-casein. Syneresis is an essential requirement in cheese making from renneted or acidified milk, but is undesirable during the storage of products such as yogurt. Milk for yogurt manufacture is preheated to minimize syneresis and to give maximal firmness of the yogurt coagulum (Tamime &amp; Deeth, 1980). Pearseet al.(1985) showed that the reduction of one-third in the extent of syneresis caused by heating artificial micelle milk (AMM) containing βlactoglobulin (β-lg) in natural concentrations was due to sulphydryl-mediated complex formation between β-lg and micellar κ-casein which appeared to interfere with the micelle–micelle interactions responsible for syneresis. The results presented here were part of a study which investigated the effects of κcasein and κ-lg genetic variants and concentrations on syneresis of curd formed from renneted heated AMM.