Lutein Is Stable in Strawberry Yogurt and Does Not Affect its Characteristics

ABSTRACT:  The impact of various levels of lutein on the physicochemical, microbiological, and sensory characteristics of yogurt over its shelf life was determined. Nonfat strawberry yogurts were prepared with 0, 0.5, 1.5, and 3.0 mg lutein per 170 g serving (20% overages were included to account for processing losses). The lutein was incorporated prior to homogenization of the yogurt mix. Stability of lutein, viscosity, pH, syneresis, standard plate counts, coliform counts, color (L*, a*, b*), and sensory evaluation (flavor, body and texture, and appearance and color) were measured at weeks 0, 1, 3, and 5 after product manufacture. The interaction effect between levels of lutein and storage time was significant for a* (redness-greenness) values. Lutein levels remained above target throughout the 5-wk storage study. Lutein did not affect viscosity, pH, syneresis, L* (lightness) and b* (yellowness-blueness) values, standard plate counts, coliform counts, flavor, body, texture, appearance, and color scores. These results suggested that lutein was suitable for inclusion in functional yogurts. The skin and eye health benefits provided by lutein can easily be incorporated into yogurt to complement inherent nutritional properties.     

Quality attributes of a heart healthy yogurt

The objective was to study the effect of heart healthy nutrients on the physico-chemical, microbiological and sensory characteristics of yogurt. Thiamine (vitamin B₁), riboflavin (vitamin B₂), niacin (vitamin B₃), folic acid (vitamin B₉), manganese and magnesium were added during mix preparation at 0%, 30%, 60% and 90% of their respective recommended dietary allowance (RDA). Fiber (Ceolus Fiber DF-17) was added at a constant rate of 176 g/7.570 kg yogurt mix in all the treatments. Total solids in the control were kept constant with non-fat dry milk. Incorporation of the heart healthy nutrients at the 30%, 60% and 90% RDA significantly decreased syneresis, pH, L*, a* values but significantly increased b* value. Product viscosity was significantly increased by the incorporation of the nutrients at 60% of their respective RDA's. The incorporation of the above heart healthy vitamins and minerals at any of the studied rates in yogurts did not significantly affect flavor, appearance, body and texture and microbial counts of the product. Although there were subtle yet significant changes in instrumental color and viscosity these slight changes could not be detected by sensory evaluation. Yogurts can successfully be manufactured with the above heart healthy nutrients.     

Fat-free plain yogurt manufactured with inulins of various chain lengths and Lactobacillus acidophilus

ABSTRACT:  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.     

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.     

Microbial, physical and sensory properties of yogurt supplemented with lentil flour

In this study, skim milk (9.5% w/v solid content) was supplemented with 1-3% (w/v) lentil flour or skim milk powder, inoculated with a yogurt culture, fermented and stored at 4 °C. Acid production during the fermentation, microbial growth, physical properties (pH, syneresis, and color), rheological properties (dynamic oscillation temperature sweep test at 4-50 °C), during 28 days of refrigerated storage and also sensory properties (flavor, mouth feel, overall acceptance and color) after production, were studied. Milk supplementation with 1-3% lentil flour enhanced acid production during fermentation, but the microbial population (CFU) of both S. thermophilus and L. delbrueckii subsp. bulgaricus were in the same range in all lentil flour and skim milk powder supplemented yogurts. The average pH of samples decreased from 4.5 to 4.1 after 28 days storage. Syneresis in 1-2% lentil flour supplemented yogurts was significantly higher than all other samples; however, greater lentil supplementation (3%) resulted in the lowest syneresis during the 28 days storage. With respect to color, “a” and “L” values did not significantly differ in all samples and remained constant after 28 days whereas “b” value increased as a result of lentil supplementation. Yogurt with 3% lentil flour showed higher storage (G') and loss (G?) moduli in comparison with samples supplemented with 1-3% skim milk powder and the non-supplemented control yogurt. Storage modulus (G') was higher than loss modulus (G?) in all samples and at all temperatures between 4 and 50 °C and they showed a hysteresis loop over this temperature range when the samples were heated and cooled. 1-2% lentil flour supplemented yogurt showed comparable sensory properties in comparison with 1-2% skim milk powder supplemented yogurt and the control sample.     

Use of acid whey protein concentrate as an ingredient in nonfat cup set-style yogurt

Acid whey resulting from the production of soft cheeses is a disposal problem for the dairy industry. Few uses have been found for acid whey because of its high ash content, low pH, and high organic acid content. The objective of this study was to explore the potential of recovery of whey protein from cottage cheese acid whey for use in yogurt. Cottage cheese acid whey and Cheddar cheese whey were produced from standard cottage cheese and Cheddar cheese-making procedures, respectively. The whey was separated and pasteurized by high temperature, short time pasteurization and stored at 4°C. Food-grade ammonium hydroxide was used to neutralize the acid whey to a pH of 6.4. The whey was heated to 50°C and concentrated using ultrafiltration and diafiltration with 11 polyethersulfone cartridge membrane filters (10,000-kDa cutoff) to 25% total solids and 80% protein. Skim milk was concentrated to 6% total protein. Nonfat, unflavored set-style yogurts (6.0 ± 0.1% protein, 15 ± 1.0% solids) were made from skim milk with added acid whey protein concentrate, skim milk with added sweet whey protein concentrate, or skim milk concentrate. Yogurt mixes were standardized to lactose and fat of 6.50% and 0.10%, respectively. Yogurt was fermented at 43°C to pH 4.6 and stored at 4°C. The experiment was replicated in triplicate. Titratable acidity, pH, whey separation, color, and gel strength were measured weekly in yogurts through 8 wk. Trained panel profiling was conducted on 0, 14, 28, and 56 d. Fat-free yogurts produced with added neutralized fresh liquid acid whey protein concentrate had flavor attributes similar those with added fresh liquid sweet whey protein but had lower gel strength attributes, which translated to differences in trained panel texture attributes and lower consumer liking scores for fat-free yogurt made with added acid whey protein ingredient. Difference in pH was the main contributor to texture differences, as higher pH in acid whey protein yogurts changed gel structure formation and water-holding capacity of the yogurt gel. In a second part of the study, the yogurt mix was reformulated to address texture differences. The reformulated yogurt mix at 2% milkfat and using a lower level of sweet and acid whey ingredient performed at parity with control yogurts in consumer sensory trials. Fresh liquid acid whey protein concentrates from cottage cheese manufacture can be used as a liquid protein ingredient source for manufacture of yogurt in the same factory.     

An excessively high Lactobacillus acidophilus inoculation level in yogurt lowers product quality during storage

The effect of manufacturing yogurt with a wide variation in Lactobacillus acidophilus inoculation level while holding the yogurt culture inoculation level constant on the properties of the resulting yogurt was determined to find out if any problems can occur if an excessively high level of L. acidophilus is used in yogurt production. Four batches of plain, set-style yogurt were manufactured with skim milk, nonfat dry milk, yogurt cultures, and with or without L. acidophilus (0, 0.0239, 0.238, or 2.33 g/100 g). After homogenization, pasteurization, and cooling, yogurt mixes were inoculated, poured into containers, incubated to pH 4.5, and cooled. Lactobacilli and L. acidophilus counts, pH, amount of syneresis, color, apparent viscosities, and sensory scores were determined during storage. The yogurt inoculated with 0.238 g/100 g L. acidophilus had the highest L. acidophilus counts from 4 to 7 wk. Yogurts inoculated with 2.33 g/100 g L. acidophilus generally had lower lactobacilli counts, L* values, apparent viscosities, and sensory scores but more syneresis and higher a* and b* values than the remaining yogurts. An excessively high inoculated level of L. acidophilus (2.33 g/100 g) resulted in an inferior quality yogurt.     

Fat free plain set yogurts fortified with various minerals

Seven different minerals (iron, magnesium, zinc, manganese, molybdenum, chromium and selenium) were incorporated separately into the yogurt mixes at 25% of their recommended dietary allowances of 15 mg, 420 mg, 15 mg, 5 mg, 200 μg, 200 μg, 70 μg, respectively. The various attributes studied on the yogurts were viscosity, syneresis, color/lightness (L*), body and texture, appearance and flavor. No significant (P>0.05) difference was observed for viscosity of the yogurts fortified with minerals when compared to the control. Yogurts fortified with iron, selenium and magnesium had better water-holding capacities compared to the control. No significant (P>0.05) differences were observed for flavor and appearance scores of the yogurts fortified with the minerals compared to the control. Fortification of yogurts with these minerals can be accomplished without adversely affecting product characteristics.     

Effects of Extruded Sugar Bagasse Blend on Yogurt Quality

Extruded blends (EB) of whey protein concentrate 35 (WPC 35)–corn starch–sugarcane bagasse with 0%, 25%, and 50% substituted yogurt formulations were evaluated for some functional characteristics. Yogurts substituted with EB showed higher viscosity and lower syneresis index than that without EB. During storage for 48 h, the syneresis values of yogurt with and without EB decreased. The pH values and color differences (ΔE) decreased slightly in the yogurts formulated with EB. However, the color differences were not statistically significant (p > 0.05) and were also acceptable to the judges. In general, yogurts substituted with EB at different levels had sensory attributes of taste, acidity, texture, and viscosity scores similar to those observed for yogurt with no EB. Scores of yogurts were not affected significantly with substitution of EB at all the levels.     

Industrial yogurt manufacture: monitoring of fermentation process and improvement of final product quality

Lactic acid fermentation during the production of skim milk and whole fat set-style yogurt was continuously monitored by measuring pH. The modified Gompertz model was successfully applied to describe the pH decline and viscosity development during the fermentation process. The viscosity and incubation time data were also fitted to linear models against ln(pH). The investigation of the yogurt quality improvement practices included 2 different heat treatments (80°C for 30 min and 95°C for 10 min), 3 milk protein fortifying agents (skim milk powder, whey powder, and milk protein concentrate) added at 2.0%, and 4 hydrocolloids (κ-carrageenan, xanthan, guar gum, and pectin) added at 0.01% to whole fat and skim yogurts. Heat treatment significantly affected viscosity and acetaldehyde development without influencing incubation time and acidity. The addition of whey powder shortened the incubation time but had a detrimental effect on consistency, firmness, and overall acceptance of yogurts. On the other hand, addition of skim milk powder improved the textural quality and decreased the vulnerability of yogurts to syneresis. Anionic stabilizers (κ-carrageenan and pectin) had a poor effect on the texture and palatability of yogurts. However, neutral gums (xanthan and guar gum) improved texture and prevented the wheying-off defect. Skim milk yogurts exhibited longer incubation times and higher viscosities, whereas they were rated higher during sensory evaluation than whole fat yogurts.     

Probiotic viability and storage stability of yogurts and fermented milks prepared with several mixtures of lactic acid bacteria

Currently, the food industry wants to expand the range of probiotic yogurts but each probiotic bacteria offers different and specific health benefits. Little information exists on the influence of probiotic strains on physicochemical properties and sensory characteristics of yogurts and fermented milks. Six probiotic yogurts or fermented milks and 1 control yogurt were prepared, and we evaluated several physicochemical properties (pH, titratable acidity, texture, color, and syneresis), microbial viability of starter cultures (Lactobacillus delbrueckii ssp. bulgaricus and Streptococcus thermophilus) and probiotics (Lactobacillus acidophilus, Lactobacillus casei, and Lactobacillus reuteri) during fermentation and storage (35 d at 5°C), as well as sensory preference among them. Decreases in pH (0.17 to 0.50 units) and increases in titratable acidity (0.09 to 0.29%) were observed during storage. Only the yogurt with S. thermophilus, L. delbrueckii ssp. bulgaricus, and L. reuteri differed in firmness. No differences in adhesiveness were determined among the tested yogurts, fermented milks, and the control. Syneresis was in the range of 45 to 58%. No changes in color during storage were observed and no color differences were detected among the evaluated fermented milk products. Counts of S. thermophilus decreased from 1.8 to 3.5 log during storage. Counts of L. delbrueckii ssp. bulgaricus also decreased in probiotic yogurts and varied from 30 to 50% of initial population. Probiotic bacteria also lost viability throughout storage, although the 3 probiotic fermented milks maintained counts ≥10⁷ cfu/mL for 3 wk. Probiotic bacteria had variable viability in yogurts, maintaining counts of L. acidophilus ≥10⁷ cfu/mL for 35 d, of L. casei for 7 d, and of L. reuteri for 14 d. We found no significant sensory preference among the 6 probiotic yogurts and fermented milks or the control. However, the yogurt and fermented milk made with L. casei were better accepted. This study presents relevant information on physicochemical, sensory, and microbial properties of probiotic yogurts and fermented milks, which could guide the dairy industry in developing new probiotic products.     

Chia (Salvia hispanica L.) seed mucilage as a fat replacer in yogurts: Effect on their nutritional,technological, and sensory properties

Growing consumer demand for healthy and nutritious products has motivated scientists and food manufacturers to design novel dairy products with higher fiber levels and lower fat content that are free of chemical additives. Chia seed mucilage (CSM) is a healthy natural gel extensively used as a dietary source of soluble fiber, a bulking agent, and a fat replacer in a large variety of foods. In this study, we evaluated the effect of CSM on the nutritional, technological, and sensory properties of skimmed yogurts. The addition of 7.5% CSM to a yogurt formula lowered the degree of syneresis of the resulting yogurt during storage compared with full-fat yogurts. The nutritive value of the enriched yogurts improved due to higher levels of dietary fiber compared with full-fat and skimmed yogurts. Moreover, rheological measurements revealed greater consistency, firmness, and viscosity, as well as the formation of a highly structured network and better resistance to stress in yogurts containing 7.5% CSM. The sensory acceptance of the yogurts enriched with 7.5% CSM was similar to the reference samples in acidity, creaminess, and viscosity terms. These results confirm the feasibility of using CSM as a fat replacer to design novel skimmed yogurts.     

Oxidative stability of yogurt with added lutein dye

This study evaluated the effect of adding lutein dye on the oxidative stability of yogurt during 35 d of refrigerated storage, in the presence and absence of light. Yogurts manufactured without and with the equivalent of 1.5 mg of lutein in 120 g of the final product were characterized for their total carotenoid and riboflavin contents, and the behaviors of both riboflavin and lutein were monitored during storage. A decrease in riboflavin content occurred, with concurrent appearance of its derived-oxidation products in the yogurts without added lutein and exposed to light during storage. The yogurts with added lutein dye showed constant lutein and riboflavin contents throughout storage both for the samples stored under light and for those stored in the dark. Yogurts (120 g) with the addition of 0.5, 1.5, and 2.5 mg of lutein dye were evaluated for their sensory acceptance, and the statistical analysis showed no differences between the samples for the attributes of aroma and flavor. These results indicate that the added lutein remained stable throughout the storage period and conferred protection for the riboflavin against photooxidation, preserving the quality of the yogurts.     

Rheological and sensory performance of a protein-based sweetener (MNEI), sucrose,and aspartame in yogurt

Sweeteners and flavors are generally added to yogurt to make them more palatable. However, the addition of these ingredients may affect the fermentation process of yogurt as well as its physical and sensory characteristics. Consumers prioritize yogurt products that are “natural.” A modified single-chain form of the natural sweet protein monellin extracted from the fruit of Dioscoreophyllum cumminsii, called MNEI, could be a useful alternative to artificial sweeteners. The aim of the present work was to evaluate new rapid sensory methods in combination with rheology to assess the viability of using MNEI to develop sweetened yogurts without the calories of sugar. We studied the gelation and cooling kinetics of 4 yogurt samples (unsweetened or sweetened with MNEI, aspartame, or sucrose) by using a rheometer. Furthermore, the 4 yogurts, with and without addition of a flavoring agent, were characterized from a sensory perspective using a combination of 2 rapid sensory methods, ultra flash profile and flash profile. Rheological results showed that, when added at typical usage levels, aspartame, sucrose, and MNEI did not generally affect the yogurt fermentation process or its rheological properties. Sensory results demonstrated that texture attributes of yogurts with aspartame and sucrose were strongly linked to sweetness and flavor perception, but this was not true for MNEI-sweetened yogurts. In contrast to results obtained from samples sweetened with sucrose and aspartame, MNEI protein did not sweeten the yogurt when added before fermentation. This study highlights the enhancing effect of flavor on sweetness perception, supporting previous reports that noted synergistic effects between sucrose or aspartame and flavors. Hence, future studies should be conducted to determine how sweet proteins behave in yogurt when added after fermentation.     

Evaluation of physical properties during storage of set and stirred yogurts made from ultra-high pressure homogenization-treated milk

The effects of ultra-high pressure homogenization (UHPH) on cow's milk were investigated and its suitability for yogurt manufacturing was compared with the conventional process currently applied in the yogurt industry. Yogurts were prepared from UHPH-treated milks at 200 and 300 MPa at 40 °C, and yogurts prepared from heat-treated milk at 90 °C for 90 s, homogenized at 15 MPa and enriched with 3% of skim milk powder were used as control samples. This study included determination of titrable acidity, water-holding capacity (WHC), and textural and rheological evaluation of gels in both set-type and stirred yogurts. In order to follow the evolution of yogurts during storage at refrigeration temperature (4–6 °C), all analyses were carried out weekly (1, 7, 14, 21 and 28 days). Results showed that yogurts from UHPH-treated milk presented higher WHC and firmness values compared with the conventional yogurts. However, the disruption of the network from UHPH-treated milk into stirred gels resulted in yogurts with higher consistency, less syneresis but coarser structure than the conventional ones.     

Syneresis and rheological behaviors of set yogurt containing green tea and green coffee powders

This study aimed to investigate the effect of added green coffee powder (GCP) and green tea powder (GTP) on syneresis behavior and consistency of set yogurts. Adding GCP (1 or 2%) decreased syneresis rate. The effect of GTP on the syneresis rate was concentration dependent. In comparison to the control, GTP decreased syneresis rate when it was added at 0.02%, but it caused an increase when added at 2%. No significant difference was observed in the syneresis rates when GTP was added at 1 and 0.01%, until 14 and 7 d of storage, respectively. The Herschel-Bulkley model parameters indicated that the consistency of control was considerably lower than that of GCP yogurts during 14 d, whereas it was higher at the end of storage. The GTP yogurt results showed that the consistency coefficients of GTP yogurts were different from those of control samples until 14 d of storage. In conclusion, GTP and GCP behaved differently in acidified gel networks of set yogurt, modifying its rheological behavior, as they have different profiles and concentrations of polyphenols.