Plain Yogurt Research Articles

Microstructure Analysis of Dried Yogurt: Effect of Different Drying Methods

Most food contains protein, fat, carbohydrate, and water, which form a food's microstructure. Processing methods, however, change the microscopic structure of the food material. This has a strong influence on final product properties, such as rheology, glass transition, moisture sorption, and so on. In this work, plain yogurt was selected as a model food to analyze microscopic structural changes after processing using different drying methods: air, vacuum, freeze, and microwave vacuum drying. Structural changes were analyzed using a scanning electron microscope and an X-ray diffraction pattern. Dried yogurt exhibits an amorphous type molecular structure in all four types of drying methods adopted. In addition, FTIR analysis showed no quantitative difference in their composition by adopting different drying methods. The moisture sorption characteristics of the dried yogurt were also studied. Sorption data were fitted into a GAB-model equation with a high correlation coefficient of 0.99.

A real-time PCR method targeting a gene sequence encoding 16S rRNA processing protein, rimM, for detection and enumeration of Streptococcus thermophilus in dairy products

Abstract A real-time PCR method targeting a gene sequence encoding 16S rRNA processing protein, rimM, for specific detection of Streptococcus thermophilus was developed. The designed real-time PCR primers and probe were specific for S. thermophilus JCM20026, LMG6896, LMG18311, OJT101, OJT102 but not Enteroccocus spp., Lactococcus lactis subsp. lactis, and Streptococcus salivarius which are phylogenetically closely related to S. thermophilus and are difficult to identify using culture-based methods. The linear range of the developed real-time PCR method was from 2.7 to 8.6 log CFU ml −1 with an amplification efficiency of 96%. Minor differences (about 0.4 log CFU ml −1 ) were observed between counts of S. thermophilus obtained by culture and real-time PCR method in plain yoghurt and yoghurt containing fruits. Therefore, the developed real-time PCR method could be of potential application in specific detection and accurate enumeration of S. thermophilus in a wide range of dairy products.

Behaviour of volatile compounds during the shelf life of yoghurt

The production of acetaldehyde, diacetyl and ethanol was evaluated in whole plain yoghurts manufactured with commercial starter cultures, yoghurt acquired in a local market, and milk fermented by a single culture of either Streptococcus thermophilus or Lactobacillus delbrueckii ssp. bulgaricus. The headspace technique was used for sample preparation, following identification and quantification by gas chromatography. During an 8‐h incubation period, mixed cultures were the most efficient in lowering the pH (from 6.30 to 4.8), followed by S. thermophilus (from 6.30 to 5.18) and L. bulgaricus (from 6.30 to 5.8). During the storage period, however, a single culture of L. bulgaricus decreased the pH more than S. thermophilus, but still less than the mixed commercial cultures. Plain yoghurts acquired in the market, those made with commercial starter cultures, and fermented milks obtained with single cultures showed, after 21 days of storage, concentrations of acetaldehyde from 11 to 35 mg/L, and of diacetyl from 0 to 0.85 mg/L. An increasing concentration of ethanol was observed during the storage period, and its production was observed even in the incubation stage of all products. It was also observed that the acetaldehyde concentration was inversely correlated to ethanol production in some products. The combination of headspace, identification and quantification techniques by gas chromatography in this work was efficient in the identification and quantification of the major aromatic compounds and ethanol content of yoghurt.

Effect of ingredients on oxidative stability of fish oil‐enriched drinking yoghurt

AbstractThe oxidative stabilities of fish oil‐enriched milk and fish oil‐enriched drinking yoghurt were compared by following the development of lipid oxidation in plain milk, plain yoghurt and yoghurt to which ingredients present in drinking yoghurt were added one by one. All samples were enriched with 1 wt‐% fish oil. After 3 weeks of storage, development of peroxide values, volatile secondary oxidation products and fishy off‐flavors were much more pronounced in the milk compared to any of the yoghurt samples, irrespective of any added ingredients used to prepare flavored drinking yoghurt. Thus, pectin, citric acid or glucono‐delta‐lactone did not affect the oxidative stability of fish oil‐enriched yoghurt emulsions. Furthermore, the fruit preparation and added sugar did not lead to increased antioxidative activity. It is concluded that yoghurt as the dairy component in the fish oil‐enriched emulsion was responsible for the remarkably high oxidative stability and was able to protect the n‐3 PUFA against oxidative deterioration. It should be considered that this strong antioxidative effect of yoghurt might mask potential antioxidative effects of the other ingredients in the drinking yoghurt.

Quality of Irradiated Plain Yogurt during Storage at Different Temperatures

To develop a safer yogurt for immuno-compromised or allergy patients and to extend shelf-life, a plain yogurt was irradiated with doses of 0, 1, 3, 5, and 10 kGy using a gamma ray and the chemical and microbiological quality and allergenicity change were investigated. There was no difference in the content of protein, total solid, and amino acids of the plain yogurt by irradiation treatment and different storage temperatures (4, 20, and 35°C). The lactic acid bacterial counts of irradiated plain yogurt had approximately 3-decimal reduction at 3 kGy, and no viable cell at 10 kGy regardless of storage time and temperature. The binding ability of rabbit antiserum to milk proteins in irradiated plain yogurt showed that 10 kGy of irradiation produced significantly higher binding ability than other treatments. Sensory evaluation indicated that only appearance of the plain yogurt irradiated at 3 kGy or higher had a lower value than the non-irradiated control when stored at 20°C. Results suggest that irradiation of plain yogurt does not significantly affect the chemical and sensory quality of plain yogurt, but can extend the shelf-life, possibly reduce allergenicity, and provide a safer product.

안전성 향상을 위해 감마선 조사한 시판 플레인 요구르트의 품질 특성

To develop a yogurt for sensitive consumer such as infants, children or immuno-compromised patients using gamma irradiation, the effects of gamma irradiation on the microbiological, chemical, and sensory quality in a commercial plain yogurt were investigated. No viable coliform bacteria were detected in the sample and approximately a 6 decimal reduction was achieved in the number of total aerobic bacteria by irradiation at 5 kGy. The initial population of lactic acid bacteria observed in the commercial plain yogurt was 8.95 log CFU/g. Gamma irradiation significantly reduced the initial microbial level to 6.47 and 2.85 log CFU/g after irradiation at 1 and 3 kGy, respectively (p

Biocontrol of dairy moulds by antagonistic dairy yeast Debaryomyces hansenii in yoghurt and cheese at elevated temperatures

Some strains of the yeast Debaryomyces hansenii are known to be antagonistic toward moulds. In this study, we describe the inhibitory effects of a dairy strain of D. hansenii as a biocontrol agent against a number of dairy moulds in plain yoghurt and cheese under non-refrigerated conditions. This antagonistic yeast showed inhibition of growth of the following dairy moulds: Aspergillus sp., Byssochlamys fulva, Byssochlamys nivea, Cladosporium sp., Eurotium chevalieri, Penicillium candidum and Penicillium roqueforti. However, the inhibitory effect of this antagonistic yeast against dairy moulds is dependent upon the concentration of the moulds: the lower the concentration, the more effective the yeast. The findings of this study have implications for both cheese maturation and dairy biopreservation. Good manufacturing practice and hygiene to keep the contaminant load down is essential for the prevention of dairy spoilage.

MICROBIOLOGICAL RESEARCH ON SOME DAIRY PRODUCTS

One hundred samples of dairy products (25 each) of UHT milk, plain yoghurt, fruit yoghurt and white soft cheese samples were examined for total viable count, and the presence of foodborne pathogenic microorganisms. The results declared that the mean total bacterial counts/ml or gm were 2.9 x104 and 7.8 x104 in examined UHT milk and white soft cheese samples, respectively. Staphylococci, Enterococci, E. coli, and Clostridium perfringens were detected in (0.0, 28.0, 40.0 and 64.0 %) & (16.0, 20.0, 36.0 and 48.0 %) & (0.0, 20.0, 28.0 and 28.0 %) and (8.0, 0.0, 0.0 and 12.0 %) of examined samples, respectively. The mean values of isolated organisms/mL or gm were (0, 1.2 x103, 1.3 x103 and 3.4 x103) & (1 x103, 1.4 x103, 1.98 x103 and 1.95 x103) & (0, 7.6 x102, 2.2 x103 and 2.1 x103) and (0.9 x103, 0, 0 and 3.3 x103), respectively. The predominant isolated bacterial stains were Staphylococcus aureus, Staphylococcus epidermidis, Enterococcus faecalis, Enterococcus faecium, Enterococcus durans, E. coli, and Clostridium perfringens by frequency distribution of (0.0, 21.7, 12.9 and 20.4 %) & (0.0, 26.2, 29.0 and 26.5 %) & (28.6, 21.7, 19.4 and 10.2 %) & (42.8, 8.7, 12.9 and 14.3 %) & (0.0, 0.0, 3.2 and 8.2 %) & (0.0, 21.7, 22.6 and 14.3 %) and (28.6, 0.0, 0.0 and 6.1 %) of total isolates, respectively. Meanwhile, Campylobacter jejuni and Salmonellae failed to be detected in all examined samples. The sanitary and public health importance of these organisms as well as control measures to improve the quality of dairy products and to safeguard the consumers from infection were discussed

DEVELOPMENT OF A SENSORY LEXICON FOR CONVENTIONAL MILK YOGURT IN THE UNITED STATES

ABSTRACT Ten trained panelists determined that 61 characteristics explained the flavor, aroma, texture, basic taste(s), feeling factors and appearance attributes inherent in 12 commercially produced yogurts formulated from bovine milk. When 12 yogurts were used to validate the sensory lexicon, differences (P < 0.05) existed in 37 of the original 61 characteristics. Yogurt brands were then differentiated based on these sensory attributes utilizing principal components analysis. This analysis revealed which attributes were most important in both explaining plain yogurt as well as allowed the clustering of different brands into groups based on taste, aroma, appearance and/or texture. Taste and texture characteristics were more effective at differentiating yogurt treatments than aroma and appearance. Even though taste and texture characteristics allowed trained panelists to identify, differentiate and categorize products, the yogurt could not be differentiated or categorized by fat percentage or source of milk (organic versus conventional).PRACTICAL APPLICATIONSA sensory lexicon was developed that is effective in the characterization and differentiation of nonflavored yogurts. Flavor and texture attributes were effective at differentiating yogurts, but yogurt products could not be grouped together according to sensory descriptors based on fat percentage and milk source (organic versus conventional).

The effect of high pressures on the yoghurt from milk with the stabilizer

The effect of high pressures on the microbiological and physio-chemical properties of yoghurt was investigated. The best results were obtained when the yoghurt was manufactured from milk with the addition of MYO 752 stabilizer (starch, gelatin, pectin) selected from 10 stabilizers. Yoghurt manufactured with the addition of 0, 6% MYO 752 stabilizer was processed at the pressure of 400-600 MPa/15 min. in the range of 50 MPa. Pressurization caused a total reduction of number of Lactobacillus delbrueckii ssp. Bulgaricus and reduced the number of Streptococcus thermophilus by 1-2 orders of magnitude. Pressurized and non-pressurized yoghurts characterized of a homogenous consistency and typical plain yoghurt taste. The decrease of the number of living bacteria was observed in yoghurts during the storage. The acidity of pressurized yoghurts remained on the some level at the temperature of 4°C and 20°C. The more intensive antibacterial activity of microflora was observed in yoghurts storaged at 20°C in comparison with yoghurts storaged at 4°C. Disadvantageous changes of the pressurized yoghurts consistency were not found. The taste and aroma of yoghurts remained without any changes.

Antibacterial activity of yoghurt against viridans streptococci in vitro

Objective Yoghurt consumption leads to a selective decrease in the oral level of mutans streptococci. It is not clear whether this decrease is due to the bactericidal activity of yoghurt or other mechanisms. The present study investigated the differences in susceptibility to yoghurt between several strains of viridans streptococci. Design The sources of variation were minimised, at the expense of the external validity of the study, using culture collection strains. Each strain was tested separately on five occasions in planktonic form and logarithmic growth phase. Two strains of each of the following Streptococcus species were tested: mutans, sobrinus, gordonii, oralis, parasanguinis and sanguinis. One millilitre [10 8 colony-forming units (cfu)] of each strain was incubated (37 °C, 60 min) with 9 mL of fat-free plain yoghurt containing Streptococcus thermophilus and Lactobacillus bulgaricus (10 8 and 10 7 cfu/g, respectively) in gently vortexed tubes. Survival rates were calculated every 15 min by dividing the number of viable cells, obtained using conventional laboratory procedures, by the baseline number. Results Survival rates were 8% ( S. mutans 6519T), 12% ( S. mutans 31738), 35% ( S. oralis 25671) and >50% (all other species tested) after 15 min, and 0.01% ( S. mutans) and >10% (all other species tested) after 30 min. Overall, S. parasanguinis and S. sobrinus were the most resistant species. When heat-treated yoghurt (<10 cfu/g bacteria and inactivated bacteriocins) was used, this antibacterial activity was not found. Conclusion In vitro, yoghurt with live bacteria showed selective anti-mutans activity, suggesting that the overall decrease in mutans streptococci in vivo could be due to a bactericidal effect on S. mutans but not on S. sobrinus.

Plain yoghurt launched by Benecol

Plain yoghurt launched by Benecol

EFFECT OF THERMOPHILIC LACTIC ACID BACTERIA ON THE FATE OF ENTEROBACTER SAKAZAKII DURING PROCESSING AND STORAGE OF PLAIN YOGURT

ABSTRACT Survival and growth of Enterobacter sakazakii during processing and storage of plain yogurt were investigated. Preheated rehydrated milk was inoculated with a cocktail culture of E. sakazakii (103 cfu/mL of milk) and/or with thermophilic yogurt starter culture of Lactobacillus delbrueckii ssp. bulgaricus and Streptococcus salivarius ssp. thermophilus. The inoculated milk was incubated at 40C for 5 h, then the samples were cooled and subsequently stored at 4C for up to 7 days. The results showed that E. sakazakii grew at an early stage of fermentation but declined at the end of the process. There was no significant difference between the populations of E. sakazakii in the presence or absence of lactic acid bacteria during the first 4 h of the incubation period but there was significant difference during the last hour of the incubation period. The populations of E. sakazakii decreased significantly during cooling and storage of yogurt (pH 4.2−4.7) compared with nonfermented milk samples at 4C. The presence of E. sakazakii did not have a significant effect on the growth of LAB during fermentation and storage of yogurt. The results obtained from this study indicate that the pH of yogurt and storage temperature were critical to the survival and growth of E. sakazakii in the manufacture of plain yogurt.PRACTICAL APPLICATIONS Enterobacter sakazakii prevalence in milk products and the production environment has been documented. The results obtained from this study may be of use to dairy producers to manufacture safe products using thermophilic lactic acid bacteria. These bacteria decreased the pH of milk in less than 5 h, resulting in E. sakazakii reduction. pH of yogurt during the fermentation process is a critical control point that should be monitored to produce safe products.

Anti-inflammatory properties of lactic acid bacteria producing superoxide dismutase

to the editor: We have read with interest the recent paper by Carroll et al. ([1][1]) showing that a treatment with Lactobacillus gasseri engineered to produce superoxide dismutase (SOD) reduces the spontaneous colitis observed in interleukin 10 (IL-10)-deficient mice. Four months before the authors

Survival of Lactobacillus acidophilus and Bifidobacterium animalis ssp. lactis in stirred fruit yogurts

The effect of commercial fruit preparations (mango, mixed berry, passion fruit and strawberry) on the viability of probiotic bacteria, Lactobacillus acidophilus LAFTI ® L10 and Bifidobacterium animalis ssp. lactis LAFTI ® B94 in stirred yogurts during storage (35 days) at refrigerated temperature (4 °C) was evaluated. The results showed that addition of either 5 or 10 g/100 g fruit preparations had no significant ( p>0.05) effect on the viability of the two probiotic strains except on L. acidophilus LAFTI L10 yogurt with 10 g/100 g passion fruit or mixed berry. After the addition of fruit preparation, 96% of the yogurts incorporated with fruit preparation did not exhibit a greater loss in the viability of probiotic bacteria compared to plain yogurt during the storage period. A correlation between the post-storage pH in yogurts and the survival of probiotic bacteria was observed. All the yogurts, however, contained the recommended levels of (10 6–10 7 cfu/g) probiotic bacteria at the end of 35-day shelf life.

Survival of Escherichia coli O157:H7 in yogurt drink, plain yogurt and salted (tuzlu) yogurt: Effects of storage time, temperature, background flora and product characteristics

The survival of Escherichia coli O157:H7 at 4 and 22°C in yogurt drink, plain yogurt and salted yogurt (yogurt native to Hatay, Turkey) was studied. Total aerobic plate count (TPC), total mould and yeast count, pH and titratable acidity during the storage period were measured. pH and TPC count of the samples at 22°C were significantly higher than those of samples at 4°C (P &lt; 0.01). E. coli O157:H7 survived in the products at both 4 and 22°C, whereas survival of E. coli O157:H7 was significantly lower at 4°C than at 22°C (P &lt; 0.05). Multiple linear regression models were used to determine factors affecting the survival of E. coli O157:H7.

Fat‐Free Plain Yogurt Manufactured with Inulins of Various Chain Lengths and Lactobacillus acidophilus

Inulin is a prebiotic food ingredient that increases the activity of Lactobacillus acidophilus, increases calcium absorption, and is a good source of dietary fiber. The objective was to determine the effect of short, medium, and long chain inulins on the physicochemical, sensory, and microbiological characteristics of fat-free plain yogurt containing L. acidophilus. Inulins of short (P95), medium (GR), and long (HP) chain lengths were incorporated at 1.5% w/w of the yogurt mix. Viscosity, pH, syneresis, sensory properties (flavor, body and texture, and appearance and color), L. acidophilus counts, and color (L*, a*, and b*) of yogurts were determined at 1, 11, and 22 d after yogurt manufacture. The P95 containing yogurt had a significantly lower pH than the remaining yogurts, higher flavor scores than the yogurt containing HP, and comparable flavor scores with the control. The yogurts containing HP had less syneresis than the control and a better body and texture than the remaining yogurts. Yogurts containing prebiotics of different chain lengths had comparable L. acidophilus counts with each other but higher counts than the control. However, inulins of various chain lengths did not affect viscosity, color, and product appearance. Chain length of prebiotics affected some quality attributes of probiotic yogurts.

Prediction of sensory properties of low-fat yoghurt and cream cheese from surface images

The sensory properties of 25 plain yoghurts and 18 low-fat cream cheeses were investigated by descriptive analysis. In parallel with sensory analysis digital images of sample surfaces were captured and the relationship between image properties and sensory properties were investigated. Global image features of the yoghurt and cream cheese surfaces were extracted using the Angle Measure Technique (AMT). Multivariate data analyses (Partial Least Squares Regression) were applied for investigation of the relation between digital image global features and sensory properties. For both product categories all sensory properties could be predicted with Root Mean Square Error of Cross Validation (RMSECV) for the yoghurts in the range [1.00; 1.97] and for the cream cheeses [0.29; 2.80]. For yoghurts, the largest RMSECV is for the prediction of Creaminess, indicating that it is not well predicted from structure alone. Due to covariation with appearance and structure, sensory properties relating to different modalities (taste and flavour) could also be predicted.

Specific Detection of Potentially Allergenic Kiwifruit in Foods Using Polymerase Chain Reaction

Kiwifruit (Actinidia deliciosa and Actinidia chinensis) is allergenic to sensitive patients, and, under Japanese regulations, it is one of the food items that are recommended to be declared on food labeling as much as possible. To develop PCR-based methods for the detection of trace amounts of kiwifruit in foods, two primer pairs targeting the ITS-1 region of the Actinidia spp. were designed using PCR simulation software. On the basis of the known distribution of a major kiwifruit allergen (actinidin) within the Actinidia spp., as well as of reports on clinical and immunological cross-reactivities, one of the primer pairs was designed to detect all Actinidia spp. and the other to detect commercially grown Actinidia spp. (i.e., kiwifruit, Actinidia arguta, and their interspecific hybrids) except for Actinidia polygama. The specificity of the developed methods using the designed primer pairs was verified by performing PCR experiments on 8 Actinidia spp. and 26 other plants including fruits. The methods were considered to be specific enough to yield target-size products only from the target Actinidia spp. and to detect no target-size products from nontarget species. The methods were sensitive enough to detect 5-50 fg of Actinidia spp. DNA spiked in 50 ng of salmon testis DNA used as a carrier (1-10 ppm of kiwifruit DNA) and 1700 ppm (w/w) of fresh kiwifruit puree spiked in a commercial plain yogurt (corresponding to ca. 10 ppm of kiwifruit protein). These methods would be expected to be useful in the detection of hidden kiwifruit and its related species in processed foods.

Quality attributes of yogurt with Lactobacillus casei and various prebiotics

The objective was to determine the effect of chain length of inulins on the characteristics of fat-free plain yogurt manufactured with Lactobacillus casei. Probiotic fat-free plain yogurts were manufactured using Streptococcus thermophilus, Lactobacillus bulgaricus and L. casei. The treatments were inulins of short (P95), medium (GR) and long (HP) chain lengths. The inulins were incorporated at a concentration of 1.5 g/100 g yogurt mix. Inulins of various chain lengths did not affect viscosity, L*, a*, b* and appearance of yogurts manufactured with L. casei. Yogurt with HP had less syneresis compared to the control, while yogurt with P95 had syneresis comparable to the control. Yogurt with P95 had a significantly lower pH than the control, while the pH of the yogurts with other treatments was not different from the control. Flavor scores of the control were comparable to yogurt with P95. The flavor scores for yogurts with P95 were significantly higher than for yogurts with HP. The yogurts with HP had better body and texture compared to the control and P95. Chain length of prebiotics affected some characteristics of the yogurts.