Nonfat Yogurt Research Articles

Physical, chemical and flavour quality of non-fat yogurt as affected by a β-glucan hydrocolloidal composite during storage

In this study, a possible use of β-glucan hydrocolloidal composite as a fat replacer in the manufacture of non-fat yogurts was investigated. The yogurts with added β-glucan composite were compared with non-fat yogurt without addition of β-glucan composite and the samples were analysed for physical, chemical and sensory attributes after 1, 7 or 15 d of storage. Fat and protein contents of the experimental yogurts were identical, while ash content differed. Addition of β-glucan composite did not show a significant change of pH, titratable acidity, acetaldehyde, volatile fatty acids and tyrosine contents at any storage time. Titratable acidity and tyrosine content increased significantly throughout storage. Gel firmness and water-holding capacity in the yogurts were not influenced by addition of β-glucan composite, but these variables decreased with storage time. Addition of β-glucan composite and storage time caused a decrease in whey separation. Viscosity values in the yogurts increased by addition of β-glucan composite and storage time. Sensory results indicated a preference for control yogurts; however, use of low levels of β-glucan composite in the production of non-fat yogurt gave satisfactory sensory scores. Yogurts containing 0.25% or 0.50% β-glucan hydrocolloidal composite were acceptable by expert panels and had scores similar to the control yogurt.

Quality properties of non-fat yogurt with addition of whey protein concentrate

The aim of the study was investigation of quality of fat-free, settype yoghurt made at 5% (w/w) protein level with addition of skim milk powder (SMP) and whey protein concentrate (WPC) blends. The ratio SMP/WPC in used blends was: 1/0; 2/1; 1/2; 0/1. On 1st, 7th and 21st day of refrigerated storage yoghurt was analysed for sensory properties, titrable acidity, pH, free fatty acids (FFA), acetaldehyde, and diacethyl. Also enumeration of viable L. delbrueckii ssp. bulgaricus and S. thermophilus was carried out. During the whole storage period products with SMP/WPC ratio at 1/2 and 2/1 obtained the best sensory score. Addition of WPC to yoghurt significantly decreased lactic acid concentration which positively influenced its stability during shelf life. It was shown that during storage acidity of yoghurt was growing up in concern of pH level. The acetaldehyde content tended to increase significantly in the yoghurt fortified with higher proportion of WPC opposite to diacethyl level which was the lowest in yoghurt with an SMP/WPC addition at 0/1. During storage concentration of both volatile compounds were the highest on 7th day and the lowest on 21st day. The maximum concentration of FFA was stated in products with SMP/WPC ratio 1/2. During the storage period FFA content significantly increased after 7th days and had no changed during next 14 days. The total number of yoghurt bacteria during the whole storage time was up to 1010 and did not vary depending on SMP/WPC ratio. Amount of L. delbrueckii ssp. bulgaricus was about one log cycle lower than S. thermophilus in all kinds of yoghurt.

Effects of Dried Dairy Ingredients on Physical and Sensory Properties of Nonfat Yogurt

Physical and sensory attributes are important factors that influence food acceptance and choices. In this study, sensory and texture properties of nonfat yogurts made from reconstituted skim milk powder (SMP) fortified with SMP as a control, whey protein isolate (WPI), yogurt texture improver (TI), and sodium caseinate (NaCn) were investigated over a 12-d storage period. Viscosity and syneresis were measured as physical quality parameters. Descriptive sensory analysis was carried out for each sample to determine the profiles of the products. Consumer acceptance testing (n = 143 consumers) was also conducted to measure the acceptability of yogurts; panelists were asked to rank their preference for the different yogurt samples. Differences among physical and sensory attributes of yogurts were defined. Addition of WPI improved the physical properties of yogurts, resulting in the highest viscosity and the lowest syneresis. On the other hand, yogurt with WPI did not have desirable sensory properties. The descriptive panel indicated that yogurt with WPI had the lowest fermented flavor attribute. In general, yogurts fortified with NaCn and TI displayed better physical and sensory properties than did control and WPI-fortified yogurts. Consumer testing showed that yogurts with NaCn and TI were not different from the control with regard to their flavor acceptability. Yogurts fortified with NaCn and TI were the most preferred samples by Turkish consumers.

Incorporation of microbial transglutaminase into non-fat yogurt production

This study investigated the physical, chemical and sensory characteristics of non-fat yogurts treated with microbial transglutaminase (MTGase) at varying concentrations from 0 to 0.5 g L −1. Also, the effect of enzyme inactivation prior to fermentation on the selected properties of the yogurts was studied. Acid development rate was reduced with increasing MTGase doses. Cross-linking of milk proteins by MTGase had a growth-slowing effect on yogurt starter bacteria, which was more pronounced at higher concentrations. Physical properties of the yogurts were improved by MTGase throughout 21-day storage; on the contrary, the production of acetaldehyde was slowed down by increasing MTGase concentrations during the same period. Principal component analysis (PCA) and hierarchial cluster analysis (HCA) clearly differentiated the samples with added MTGase at lower (⩽0.3 g L −1) and higher (0.4–0.5 g L −1) concentrations regarding the physical and sensory properties. The physical and sensory properties of non-fat set yogurt could be improved by incorporating MTGase up to a level of 0.3 g L −1.

Rheological Properties and Texture of Yoghurts When Oat-Maltodextrin is Used as a Fat Substitute

Yoghurts were produced from cow’s milk containing 1, 2 and 3 kg milk fat/100 kg or 1, 2 and 3kg of oat-maltodextrin/100 kg (maltodextrin included 5 kg β-glucan/100 kg). Non-fat yoghurt, without the addition of maltodextrin, was used as a control product. The yoghurts were estimated for sensory properties and using instrumental texture profile analysis (TPA) and rheological investigations, which had to set flow curves and their description by the Ostwald de Waele and Casson models; counting apparent viscosity were also done. Replacing milk fat with maltodextrin in yoghurts does not show significant differences in the sensory analysis, rheological properties and most of the texture parameters. The addition of milk fat in the amount of 1 kg/100 kg or maltodextrin in 2 kg/100 kg caused an increase in apparent viscosity of yoghurts. The addition of oat-maltodextrin caused a decrease in consistency index value and a deviation from the Newtonian flow and yield stress, similar to the effects caused by adding milk fat. No relationship between the results of the sensory evaluation, the instrumental texture parameters and rheological properties, especially in yoghurts containing milk fat, were shown

The Influence of Storage Time on Rheological Properties and Texture of Yoghurts with the Addition of Oat-Maltodextrin as the Fat Substitute

Yoghurts from cow's milk containing 2 kg milk fat/100 kg or 2 kg an oat-maltodextrin/100 kg (maltodextrin included 5 kg β-glucan/100 kg), were produced in a laboratory scale and stored in refrigerator conditions for 21 days. Non-fat yoghurt without addition of maltodextrin was used as a control product. The yoghurts were estimated after 1, 7, 14 and 21 day's storage. The sensory evaluation, instrumental texture profile analysis and rheological investigations were carried out, they included the determination of the flow curves and the description by Ostwald de Waele and Casson models as well as counting an apparent viscosity. Differences in the sensory quality of yoghurts containing milk fat or maltodextrin were not found, whereas these yoghurts were characterised by better sensory quality than the control product. The storage time had significant influence on the sensory evaluation and the texture parameters. During the storage time apparent viscosity of yoghurts decreased. A decrease in consistency index value, in deviation from Newtonian flow, and yield stress was noticed, whereas in Casson's viscosity of the yoghurts an increase was found.

Effects of Flavorings, Storage Conditions, and Storage Time on Survival of Staphylococcus aureus in Sürk Cheese

The objectives of this study were to determine the cumulative effects of flavorings (chili pepper, thyme, mint, cumin, nutmeg, allspice, clove, cinnamon, black pepper, salt, and hot red pepper paste), storage conditions, and storage time on the survival of Staphylococcus aureus in Sürk cheese and to monitor the associated chemical changes. Sürk cheese, a traditional Turkish cheese, was produced by heating diluted nonfat yogurt and adding flavorings to the resultant acid-heat curd. The cheese was later inoculated with S. aureus, shaped conically, and stored aerobically for mold growth and anaerobically in olive oil for 30 days at room temperature. The moisture content of aerobically stored cheese decreased over time and led to increases in total solids, salt, salt-in-moisture, and ash content during ripening (P < 0.05). The presence or absence of the flavorings had no significant effect, whereas storage conditions and storage duration decreased the survival of S. aureus (P < 0.05).

The Influence of Storage Time on Rheological Properties and Texture of Yoghurts with the Addition of Oat-Maltodextrin as the Fat Substitute

Yoghurts from cow's milk containing 2 kg milk fat/100 kg or 2 kg of an oat-maltodextrin/100 kg (maltodextrin included 5 kg b-glucan/100 kg), were weighed on a laboratory scale and stored in refrigerator conditions for 21 days. Non-fat yoghurt without the addition of maltodextrin was used as a control product. The yoghurts were analysed after 1, 7, 14, and 21 days of storage. Sensory evaluation, instrumental texture profile analysis, and rheological investigations were carried out. They included the determination of the flow curves and the description by Ostwald de Waele and Casson models as well as an account of the apparent viscosity. Differences in the sensory quality of yoghurts containing milk fat or maltodextrin were not found, whereas these yoghurts were characterized by better sensory quality than the control product. The storage time had a significant influence on the sensory evaluation and the texture parameters. During the storage time, the apparent viscosity of yoghurts decreased. A decrease in consistency index value, in deviation from Newtonian flow, and yield stress was noticed, whereas in Casson's viscosity of the yoghurts, an increase was found.

Direct detection of bacterial pathogens in representative dairy products using a combined bacterial concentration-PCR approach

To develop a simple, rapid method to concentrate and purify bacteria and their nucleic acids from complex dairy food matrices in preparation for direct pathogen detection using polymerase chain reaction (PCR). Plain non-fat yogurt and cheddar cheese were each seeded with Listeria monocytogenes or Salmonella enterica serovar. Enteritidis in the range of 10(1)-10(6) CFU per 11-g sample. Samples were then processed for bacterial concentration using high-speed centrifugation (9700 g) followed by DNA extraction, PCR amplification, and amplicon confirmation by hybridization. Bacterial recoveries after centrifugation ranged from 53 to >100% and 71 to >100% for serovar. Enteritidis and L. monocytogenes, respectively, in the non-fat yogurt samples; and from 77 to >100% and 69 to >100% for serovar. Enteritidis and L. monocytogenes, respectively, in the cheddar cheese samples. There were no significant differences in recovery efficiency at different inocula levels, and losses to discarded supernatants were always <5%, regardless of dairy product or pathogen. When followed by pathogen detection using PCR and confirmation by amplicon hybridization, detection limits of 10(3) and 10(1) CFU per 11-g sample were achieved for L. monocytogenes and serovar. Enteritidis, respectively, in both product types and without prior cultural enrichment. This study represents progress toward the rapid and efficient direct detection of pathogens from complex food matrices at detection limits approaching those that might be anticipated in naturally contaminated products.

Potential for β-Cyclodextrin as Partial Fat Replacer in Low-fat Foods

ABSTRACT: Headspace gas chromatography analysis of a series of flavored milks and yogurts indicated that addition of β-cyclodextrin to nonfat products results in flavor-release profiles similar to those of corresponding higher-fat-content products, suggesting the potential for this material as a partial fat replacer. A follow-up sensory evaluation study was carried out with a number of yogurts and salad dressings. Although addition of β-cyclodextrin to nonfat yogurt did not result in a product more like a low-fat product (based on flavor and texture), flavor profiles of nonfat Italian-style and ranch-style dressings were indeed more similar to the corresponding full-fat products. Therefore, the use of β-cyclodextrin as a partial fat replacer in salad dressings appears worthy of further study.

Survival of Listeria monocytogenes in Vanilla-Flavored Soy and Dairy Products Stored at 8°C

The survival of Listeria monocytogenes V37 in vanilla-flavored yogurt (low-fat and nonfat) and soy milk (low-fat and Plus) stored at 8°C for 31 days was investigated. Commercial samples of yogurt and soy milk were used. These samples were inoculated with either 104 or 107 CFU of L. monocytogenes per ml. Sampling was carried out every 3 to 4 days initially and was then carried out weekly, for a total storage time of 31 days. Each time a sample was collected, the pH of the sample was measured. After 31 days, low-fat plain, low-fat vanilla, and nonfat plain yogurt samples inoculated with 104 CFU/ml showed 2.5-log reductions in viable cell populations, and nonfat vanilla yogurt showed a 3.5-log reduction. For yogurt inoculated with 107 CFU/ml, reductions of 2.5 log CFU/ml were observed for plain low-fat and nonfat yogurts, and reductions of 5 log CFU/ml were observed for vanilla-flavored low-fat and nonfat yogurts. In vanilla-flavored and plain low-fat and Plus soy milk samples, cell counts increased from 104 and 107 CFU/ml to 109 CFU/ml at 7 and 3 days of storage, respectively, at 8°C. Coagulation in soy milk samples was observed when the cell population reached 109 CFU/ml. In soy milk, the L. monocytogenes population did not change for up to 31 days. Vanillin had an inhibitory effect on L. monocytogenes in yogurt but not in soy milk.

Article

A procedure was developed for the production of a high milk protein powder that was rich in both milk proteins, casein and whey proteins, and free of lactose. The method utilized ultrafiltration and diafiltration with no pH adjustment and a relatively low temperature. Spray drying was conducted at low temperatures (120 to 125 o C inlet air temperature, 75 to 80 o C outlet air temper- ature). The resulting powder contained at least 84% total protein (casein and whey proteins). Microstructural studies of the high protein powders revealed that the surface structure of the powders became smoother as lactose was reduced. The surface of the powders with the most lactose, such as skim milk powder, had the most wrinkles. The virtual absence of lactose in this powder allows storage at room temperature for a long time without deterioration or caking. Solubility index of the powder decreased (solubility increased) as temperature of reconstitution increased from 25 to 60 o C. Foaming capacity was highest at pH 10. Because of the similarity of the proteins of this powder to those of skim milk, and due to the absence of lactose, it was possible to use it in the manufacture of nonfat yogurts with good body and texture. Traditionally, nonfat yogurts have poor body and fre- quently have excessive whey separation. Use of gelling and stabilizing agents is therefore almost mandatory. The high milk protein powder, while adding protein to yogurt, served as a stabilizer to im- prove body and texture. The suitability of this powder as a medium for bulk starter was also investi- gated. The high buffering capacity of this powder in combination with nonfat dry milk made possible the production of an active bulk starter, which was subsequently used in the manufacture of Gouda cheese.

Fun Microbiology: Making Plain &amp; Frozen Yogurt

Yogurt is one of the oldest fermented milk products known. It is believed to have originated approximately 4,000 years ago in the Middle East (the name comes from Turkish) and spread with the migration of herdsmen in search of water and pastures to stake a living (Vedamuthu 1993). Although yogurt has a long history, its popularity and growth in sales in the United States has occurred primarily over the last 20 years. This could be attributed (but not limited) to the following developments: use of sweeteners to mute tart acid flavor of plain yogurt, introduction of fruits and nuts, inclusion of low-fat and non-fat yogurts containing non-nutritive sweeteners with advertising aimed at calorie-conscious persons, introduction of frozen yogurt as a low-calorie dessert, and accumulation of scientific data indicating health benefits of yogurt consumption (Halpem et al. 1991; Isolauri et al. 1991; Pochart et al. 1989; Vedamuthu 1993). Yogurt is a solid, custard-like milk product fermented with a mixture of the bacteria Streptococcus salaivarius subsp. thermophilus (coccus shaped) and Lactobacillus delbrueckii subsp. bulgaricus (rod shaped)(Atlas 1997; Jay 1996). The pairing of coccus and rod is important in yogurt production because there is an associative beneficial relationship formed between these two bacteria, which in biology is referred to as symbiosis. Modern cultured yogurt production usually begins with concentrating milk by 1/4 volume in a vacuum pan by heating at 90? C (1940 F) for a few minutes. The milk is fortified at 380

Application of Ultrafiltered Sweet Buttermilk and Sweet Buttermilk Powder in the Manufacture of Nonfat and Low Fat Yogurts

Nonfat and low fat yogurts are soft, low in solids, and exhibit whey separation unless they are heavily stabilized. In this study, the quality of nonfat (9.55 to 10.39% total solids) and low fat (13.40%) yogurts that had been fortified with ultrafiltered sweet buttermilk or buttermilk powder was compared with that of a control yogurt that had been fortified with nonfat dry milk. The titratable acidity and pH of low fat yogurts were higher than those of nonfat yogurts. Low fat yogurt that had been fortified with ultrafiltered sweet buttermilk had the highest pH and titratable acidity. As shearing speed increased, the apparent viscosity of yogurts decreased, indicating a shear thinning property. At a high shearing speed, shearing time had little effect on the apparent viscosity. Nonfat yogurts with tested ingredients were similar to the control in flavor, appearance, texture, aroma, smoothness, and sourness. At a high level of fortification, ultrafiltered sweet buttermilk lacked typical yogurt flavor but had good appearance. The microstructures of nonfat yogurts were more open than those of low fat yogurts, possibly because of the higher protein contents of the latter. Ultrafiltered sweet buttermilk yielded the densest matrix. The addition of up to 4.8% sweet buttermilk powder to low fat yogurt mixes yielded a soft and smooth product.

Conjugated Linoleic Acid Concentrations in Dairy Products as Affected by Processing and Storage

ABSTRACTTotal conjugated linoleic acid (CLA) concentrations increased 1.32 fold in salted and 1.27 in unsalted butter but did not alter the ratio of 9‐cis 11‐trans to total CLA. Nonfat yogurt showed an increase in CLA content with processing (5.25 mg total CLA/g fat) compared to unprocessed raw material (4.40 mg CLA/g fat). No changes in CLA content was observed in processed dairy products such as lowfat yogurt, regular yogurt, lowfat and regular ice cream, sour cream or cheeses such as Mozzarella, Gouda and Cheddar. Storage did not affect CLA concentration in any products suggesting that CLA is a stable component.

Chemical, Microbiological and Sensory Properties of Plain Nonfat Yogurt

ABSTRACTChemical and microbiological properties of plain nonfat yogurt were determined after 2, 6 and 12 days refrigerated storage. Sensory properties were determined after 6 days storage. Viable culture bacteria concentrations ranged from 140 to 8,000 × 106/g and ratios of lactobacillus to streptococcus ranged from 0.18 to 15.4. Chemical criteria used to characterize products included: pH, titratable acidity, lactic and four other organic acids and lactose by HPLC, and 23 major volatile organic compounds by dynamic headspace analysis. Lactic acid concentrations ranged from 7.5 to 9.9 mg/g. Major flavor volatiles in all yogurts included: acetaldehyde, heptane, acetone, diacetyl, and benzothiazole. Untrained sensory panels showed differences for flavor, aroma and acceptability.

Manufacture of Nonfat Yogurt from a High Milk Protein Powder

Nonfat yogurts were manufactured from skim milk fortified with a new high milk protein powder. The powder, containing approximately 84% milk protein, was added to skim milk to obtain 5.2 to 11.3% total protein, 11.1 to 15% total solids, and 1.6 to 7.9% lactose in the yogurt mix. Mixes were homogenized, pasteurized at 90°C for 10min, and fermented with a yogurt culture at 42°C to pH 4.6. Controls were made from the same skim milk fortified with NDM to approximately 14% total solids. Yogurts made with the protein powder and containing 5.6% protein were similar in firmness to the control and had good flavor when fresh and after 2 wk of storage. Yogurts with more than 5.6% protein were too firm and had an astringent flavor. Acetaldehyde content of all yogurts was comparable with that of the control, and fat content ranged from .18 to .33%. As the protein content of yogurts increased, the porosity of yogurts, as seen by scanning electron microscopy, decreased. Good quality nonfat yogurts can be produced by supplementing skim milk with a high milk protein powder up to 5.6% protein The added protein assists in providing a firm body and minimal whey separation without the use of stabilizers.

Calcium Additives and Sprouted Wheat Effects on Phytate Hydrolysis in Whole Wheat Bread

ABSTRACTWhole wheat bread loaves were subjected to treatments of different fermentation periods, different sources and levels of calcium, and the addition of sprouted wheat. Phytate losses increased with increased fermentation time. Increasing the calcium level inhibited phytate hydrolysis when the calcium was provided by nonfat dry milk, CaCl2, or nonfat yogurt, whereas phytate hydrolysis in loaves supplemented with CaCO3 remained nearly constant. Milk‐derived calcium exerted the greatest inhibition of phytate hydrolysis. The addition of sprouted wheat decreased absolute phytate losses. A comparison of phytate losses in yeasted vs nonyeasted loaves suggested that endogenous wheat phytase was quantitatively more important than yeast phytase during breadmaking.

Alkylating activity in food products—especially sauerkraut and sour fermented dairy products—after incubation with nitrite under quasi-gastric conditions

N-Nitroso compounds may well rank high among the genotoxic carcinogens present in our environment. Small amounts of such compounds may be formed in the human stomach after consumption of high-nitrate vegetables. Volatile nitrosamines can be conveniently determined but reliable methods of analysis for non-volatile N-nitroso compounds are still lacking. In this study we have used the 4-(4-nitrobenzyl)pyridine test to look for the formation of alkylating compounds such as N-nitroso- N-methylurea in a wide range of food products after incubation with nitrite under simulated gastric conditions. Our results indicate that many food products do not form alkylating compounds in appreciable amounts, even though the nitrite concentration used was five to ten times that found in saliva after a high-nitrate meal. Comparatively strong alkylating activity, however, was detected after incubation of samples of sauerkraut, certain dairy products (yoghurt, biogarde, quark, buttermilk and milk), wine and smoked mackerel. Samples of sauerkraut incubated with simulated gastric fluid, but without (added) nitrite, also displayed appreciable alkylating activity. The formation of alkylating substances in non-fat yoghurt was markedly inhibited by addition of ascorbic acid. The identity of the alkylating agents remains unknown. The isolation procedure was optimized for N-nitroso- N-methylurea, but will certainly result in the isolation of other compounds, such as C-nitroso-, C-nitro- or perhaps even C-nitroso- C′-nitro-compounds, as well. Biogenic amines, glucosinolates, indole derivatives or other compounds may be involved as precursors. If alkylating agents are formed in vivo after ingestion of high-nitrate vegetables or drinking water, this is likely to occur only when the food products mentioned above are ingested simultaneously with or shortly after the nitrate load and not appreciably (except perhaps in the case of sauerkraut) when they are ingested alone, without a nitrate source. The health implications of these findings cannot yet be established. Many alkylating agents, however, have strong carcinogenic properties and continued investigation of food products (and their interaction products with nitrite) is indicated.