Jacek Domagała

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

Instrumental Texture, Syneresis and Microstructure of Yoghurts Prepared from Goat, Cow and Sheep Milk

Set-yoghurts from goat, cow, and sheep milk from middle lactation period were produced. In fresh yoghurts and after 14 days cold storage the following properties were analysed: hardness, adhesiveness, and extrusion force using instrumental texture analyzer, syneresis using drainage and centrifugal methods and microstructure using scanning electron microscope (SEM). Yoghurt from goat milk was characterized by lower hardness, adhesiveness, extrusion forces, and higher susceptibility to syneresis than yoghurts from cow and sheep milk. Microstructure of goat milk yoghurt was more delicate in comparison with microstructure of cow and sheep milk yoghurt. The composition and/or properties of goat milk for yoghurt production, or processing conditions need to be modified to obtain the proper texture and reduced syneresis in final product.

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

Yoghurts from cows 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 Cassons viscosity of the yoghurts, an increase was found.

Instrumental Texture, Syneresis, and Microstructure of Yoghurts Prepared from Ultrafiltrated Goat Milk: Effect of Degree of Concentration

The objective of this study was to determine the effect of concentration degree (1.5-fold, 2-fold, and 2.5-fold [v/v]) of ultrafiltrated goat milk on instrumental texture, syneresis, and microstructure of set-yoghurt. The milk for control yoghurt was non-concentrated. The concentration of goat milk by ultrafiltration caused an increase in the hardness, the adhesiveness, the extrusion force of yoghurt, and a reduction in the syneresis. The microstructure of yoghurts from ultrafiltrated milk showed a compact protein matrix, a small amount of void spaces, and large casein micelles in comparison to the microstructure of yoghurts from non-concentrated milk. The best texture and the smallest syneresis of goat milk yoghurts could be obtained at 1.5- or 2-fold [v/v] goat milk concentration. Yoghurt from 2.5-fold concentrated milk was characterized by a too hard and compact structure with a consistency typical for cream cheese, not yoghurt.

The influence of texture improver type and its addition level on rheological properties of goat’s milk yogurt

Set yoghurt from goat’s milk with addition of two texture improvers DSE 6693 and DSE 6694 from NZMP New Zealand, added in the amount of 1, 2and 3% and control yogurt without addition of texture improvers were produced. In yogurt determined sensory quality, pH, apparent viscosity and rheological properties. Flow curves obtained for produced yogurts were described by three rheological models: Ostwald de Waele, Herschel-Bulkley (H-B) and Casson. Addition of texture improver caused an increase in total solids and total protein content of milk for yogurt. Yogurt with texture improvers gave better sensory quality than control yogurt. The yogurt with 1% addition of DSE 6693 and with 2% addition of DSE 6694 had the best sensory quality. The increase in addition level of texture improvers caused an increase in apparent viscosity, consistency coefficient K, yield stress (except H-B model) and deviation from Newtonian flow (decrease of flow index n). Effect of type of improver was rather negligible, whereas its level addition considerably influenced the evaluated rheological parameters.

The suitability of different probiotic strains for the production of fruit-whey beverages

BACKGROUND When designing new probiotic products, one of the most important aspects is the selection of bacterial strains with high survival rates in the matrix of the product concerned. The aim of the present research was to evaluate the potential of selected strains of probiotic bacteria for the production of fruit-whey beverages. METHODS Orange, apple and blackcurrant whey beverages were produced, and each was inoculated with one of the following probiotic strains: Bifidobacterium lactis HN019TM; Lactobacillus aci- dophilus NCFM®; Lactobacillus paracasei Lpc-37TM; Lactobacillus rhamnosus HN001TM. The count of probiotic bacteria as well as pH and total acidity were evaluated at the 1st, 7th, 14th, 21st and 28th day of storage. RESULTS Beverages containing L. paracasei Lpc-37TM or L. rhamnosus HN001TM were characterized by a sig- nificantly higher average number of viable cells (7.02 or 7.05 log cfu/g, respectively) than products with lactis HN019TM or L. acidophilus NCFM® (6.43 or 6.37 log cfu/g, respectively). The use of L. paracasei Lpc-37 and L. rhamnosus HN001 strains in orange and apple drinks allows the recommended count for probiotic products, 106 cfu/g for 28 days of storage, to be exceeded. Survival of the B. lactis HN019 strain fulfills the above requirements only in the orange drink. The L. acidophilus NCFM® strain was found to be the least suitable for the production of beverages, as it did not reach 6 log cfu/g in any products after 28 days of stor- age. The highest average number of bacteria was found in the orange beverages (7.14 log cfu/g). In terms of bacteria viability, blackcurrant juice was the least suitable for the production of whey probiotic drinks, due to its high acidity. CONCLUSIONS The results of the present study indicate that careful selection of the fruit juice component, especially in terms of its acidity, is key to designing successful probiotic fruit-whey beverages. Other factors which should be taken into account to ensure a sufficient number of live probiotic cells, i.e. their therapeutic level in fruit-whey drinks, are the choice of probiotic strain and determination of the maximal shelf life.