Organoleptically, flavored yogurts appear to contain lower levels of acetaldehyde than plain yogurt. This study was undertaken to seek the reasons for this phenomenon by focusing on the analyses of acetaldehyde production by yogurt culture bacteria in yogurt base containing added sucrose and by performing other analyses such as the determination of cell numbers, pH, titratable acidity, volatile acidity and average flavor threshold (AFT) values of acetaldehyde in various media. The volatile compounds produced by yogurt culture bacteria were trapped and chromatographed by a gas entrainment on-column trapping gas-liquid chromatographic technique. Acetaldehyde was identified by coincidence of retention time with that of the authentic compound and quantitated using methyl acetate as an internal standard. Acetaldehyde production by mixed cultures was first detectably inhibited by 8% sucrose. However, acid production and cell counts of both species, grown together in the mixed culture, were inhibited by concentrations of sucrose of 4% and higher. A rapid production of acetaldehyde at concentrations between 0% and 8% sucrose occurred between 2 and 6 hr incubation times. The level of this compound then decreased up to 15 hr incubation and leveled off with continued incubation up to 24 hr. By itself, Lactobacillus bulgaricus was stimulated by 4%, 8% and 12% sucrose resulting in the high production of acetaldehyde and lactic acid and increased cell numbers in comparison with cultures grown in media containing no added sucrose. A level of 8% sucrose was most effective. The rod continuously produced acetaldehyde up to 24 hr, suggesting it is responsible for the production of high concentrations of acetaldehyde in yogurt. Acetaldehyde production by Streptococcus thermophilus varied from strain to strain. In general, however, less acid was produced and microbial numbers were lower, as sucrose content increased. The coccus produced much lower amounts of acetaldehyde at equivalent incubation times as compared with the rod. During refrigerated storage of from 1 to 14 days, acetaldehyde concentration greatly decreased in media containing both 0% and 8% sucrose. Values for volatile acidity of yogurts containing 0% to 8% sucrose were low. There was little or no difference in volatile acidities between yogurts containing 0% and 8% sucrose. Average flavor threshold values for acetaldehyde were slightly higher in 2%-fat milk with 8% added sucrose than in plain 2%-fat milk. With the addition of both strawberry flavor and 8% sucrose, the AFT of acetaldehyde was much higher. Since there were no great differences in the levels of acetaldehyde found in yogurts containing 0%, 4% or 8% sucrose (8% being the amount ordinarily added to flavored yogurt), it is suggested that the strong masking effect exerted by fruit, fruit flavor and sucrose, as demonstrated by AFT values, is largely responsible for the organoleptic sensation of lower levels of acetaldehyde in flavored yogurt. / Graduation date: 1972

Thesis, PlanA (M.S.)--University of Wisconsin--Stout, 1999. / Includes bibliographical references.

Thesis (M.S.)--Wisconsin. / Includes bibliographical references (leaves 99-118).

Thesis (M.S.)--University of Wisconsin--Madison, 1981. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 59-61).

Master of Science / Food Science Institute / Fadi M. Aramouni / Fermented dairy products have long been associated with positive health benefits. Certain probiotics, such as Lactobacillus rhamnosus, have gained popularity as a natural way to improve health and immunity. Fermented dairy products are an easy way to incorporate and deliver probiotics to the consumer. Synbiotic systems are also being investigated as a method for promoting the growth and survival of probiotic bacteria, both during fermentation and after consumption. The purpose of this research was to develop a synbiotic yogurt drink, incorporating L. rhamnosus (probiotic) and inulin (prebiotic), and to investigate the effect of the synbiotic relationship on sensory, physical, chemical, and microbiological properties over time. Yogurt drinks containing the probiotic L. rhamnosus HN001 (treatment P), inulin (treatment I), and a synbiotic system (treatment S) were tested using a randomized block design. Color, viscosity, brix, syneresis, and pH were measured throughout a shelf-life of 28 days. Consumer acceptability was also tested with middle-school aged children. A shelf-life of 28 days at refrigerated temperature was found to be acceptable for the product based on chemical, physical, and microbial analysis. Based on sensory results, the synbiotic drink was found to be acceptable to the target consumers (scoring a 6.82 in “overall liking” on a 9-point hedonic scale), though the treatment with 3% inulin scored slightly higher in most categories (scoring a 7.24 in “overall liking” on a 9-point hedonic scale).

Evalúa el efecto del polvo proteico de pota (Dosidicus gigas) como insumo en la elaboración de yogurt y sobre las características fisicoquímicas y organolépticas del yogurt. El polvo proteico de pota tiene un contenido de proteína de 42 % y presenta un efecto positivo en las características fisicoquímicas y organolépticas del yogurt elaborado, tales como: bajo pH, alta acidez y viscosidad, poca sinéresis y agradable sabor, aroma, textura y color. Utiliza 6 tratamientos (5 tratamientos con adición de 1, 3, 5, 7 y 10 % p/v, de polvo proteico de pota, y un tratamiento control). La acidez aumenta a 1,05 %, ocasionando, disminución en el pH hasta 4,06, en el yogurt elaborado (tratamiento 5). La viscosidad resulta más alta (58900 cP) y la sinéresis más baja (0,10 %) en el tratamiento 5 (10 %, p/v). La cantidad óptima de utilización del polvo proteico de pota en la elaboración de yogurt es de 3 % (p/v) (tratamiento 2) y tiene las características: pH 4,31, acidez 0,85 %, viscosidad 40933 cP y sinéresis 0,90 %. La prueba de aceptabilidad indica buena aceptación por parte de los panelistas; siendo el tratamiento 2 (3 %, p/v) la de mejor calificación promedio.

Rheological behavior of two commercial brands of stirred yogurt were investigated using a Haake RV 20 rotational viscometer. For samples from both brands, the upward shear-rate flow behavior generally followed the Herschel-Bulkley model and the downward flow curves were linear. They demonstrated progressive structural degradation with repeated shearing. In the steady shear runs, all samples exhibited apparent thixotropic behavior and did not attain the equilibrium condition even after 60 min of continuous shearing. The time-dependent stress decay behavior of all samples were accurately described by Weltman's logarithmic time model. The rheological properties of both yogurt brands were qualitatively similar. Both Arrhenius and Turian models were found suitable to assess the temperature influence in the range 10-25$ sp circ$C. / The influence of pectin (0.0 to 0.5%) and fruit concentrates (raspberry and strawberry) (64$ sp circ$B, 0 to 10%) on the rheology of stirred yogurt were evaluated. The influence of storage time at 2$ sp circ$C up to a period of four weeks on the rheological properties of the two brands were evaluated.

No description available.

Thesis (Ph. D. engineering science)--Washington State University, December 2007. / Includes bibliographical references.

Memoria para optar al título de Ingeniero en Alimentos / Chile es un gran productor de frutas y verduras, sin embargo el consumo per cápita no alcanza la ingesta recomendada por la OMS de 400 g diarios. Como respuesta y sumándose al cambio de conciencia mundial por mejorar los hábitos alimenticios, el objetivo de este estudio fue obtener una pulpa liofilizada de frambuesa y utilizarla para reemplazar colorantes y saborizantes en un yogur, ofreciendo una alternativa de producto más natural, con aporte de fruta. Se determinó un protocolo de liofilización para pulpa de frambuesa cuyo ciclo de congelación alcanza los -40°C en 135 min, seguido por un ciclo de secado primario a -15° C durante 1140 min y un secado secundario a 25°C durante 120 min, ambas temperaturas de secado se realizaron bajo una presión programada de 200 mTorr. La pulpa de frambuesa liofilizada obtenida logró una humedad de 6,9 ± 1,2 % y una actividad de agua de 0,28 ± 0,07. Para la determinación de la fórmula óptima de yogur con pulpa liofilizada fue necesaria la formación de un panel entrenado, constituido por 10 alumnos de la carrera de Ingeniera de Alimentos de la Universidad de Chile. Como diseño experimental se aplicó un modelo central rotacional compuesto (22+estrella) con tres puntos centrales, con 11 corridas experimentales, usando como factores la concentración de pulpa (1 a 10 g) y azúcar (5 a 60 g) en una matriz de yogur natural, y seis variables de respuesta de calidad sensorial. La optimización conjunta de los atributos sensoriales: color, aroma, consistencia con cuchara, sabor y textura bucal, arrojó una concentración óptima de 18% de azúcar y 4% de pulpa liofilizada de frambuesa. Con esta formulación optimizada se realizó una prueba con consumidores (N=48) frente a una marca comercial (Next trozo frambuesa de Soprole), donde la muestra correspondiente al yogur con pulpa de frambuesa liofilizada obtuvo preferencia significativa de 66%, y buenos indicadores de aceptabilidad / Chile is a great producer of fruits and vegetables, nevertheless the consumption per capita does not reach the daily intake of 400 g recommended by the World Health Organization. In response and adding up to the change in global awareness to improve eating habits, the purpose of this study was to obtain a freeze-dried raspberry pulp and use it to replace colorants and flavoring in a yogurt, offering an alternative product more natural and more contribution of the fruit itself. A protocol was determined by lyophilization (freeze - drying) of raspberry pulp which freeze cycle reaches -40°C in 135 min, followed by a primary drying cycle at -15°C for 1140 min and a secondary drying at 25°C for 120 min. Both drying temperatures were performed under a pressure of 200 mTorr. The obtained freeze – dried raspberry pulp achieved moisture of 6.9 ± 1.2% and a water activity of 0.28 ± 0.07. To determine the optimal formula of yogurt with freeze-dried pulp was necessary the constitution of a trained panel, consisting of 10 students from the Food Engineering career imparted by the University of Chile. As an experimental design, a compound rotational central model was applied (22 + star) with three central points, with 11 experimental runs, using pulp concentration (1 to 10 g) and sugar (5 to 60 g) as factors in a natural yogurt matrix and six quality sensory response variables. The joint optimization of the sensory attributes: color, aroma, spoon consistency, taste and mouth texture, displayed an optimal concentration of 18% sugar and 4% freeze-dried raspberry pulp. With this optimized formulation a test with consumers was made (N= 48) comparing with trademark product (Next Trozo Frambuesa, Soprole). The sample of the yogurt with raspberry pulp lyophilized had a significant preference of 66% with good indicators of acceptability