Optimization of the Rheological and Sensory Properties of Stirred Yogurt as Affected by Chemical Composition and Heat Treatment of Buffalo Milk

Abstract

The effects of fat content and the supplementation of milk with Sodium Caseinates (SCN) and Whey Proteins Concentrates (WPC) on the rheological and sensory properties of stirred yogurt made from buffalo milk were investigated. Whether the heat treatment of the milk affected the rheological behavior and the sensory characteristics of the samples was also evaluated. Principal Component Analysis (PCA) was used to assess in detail the relative contribution of whey proteins, caseins and fat on the rheological properties and sensory characteristics of the samples. Furthermore, it related the instrumental and objective sensory data to consumer perception (hedonic response of non-trained panelists). The objective acidity and white color intensity were positively correlated and increased with increasing casein content. Fat interacted synergistically with caseins to increase all the hedonic attributes, apart from odor. As far as rheological properties are concerned, elastic modulus (G'), instantaneous elasticity (G g ), retarded elasticity (G R ) and Newtonian viscosity (η 0 ) were positively correlated with increasing casein content. However, tan δ was negatively correlated with the aforesaid attributes and increased with increasing fat content. Whey proteins in the presence of fat determined the magnitude of flow behavior index (n). The lactic acid concentration (%) and the b component of color (yellow color intensity) were affected positively by SCN and WPC addition but in the absence of fat. In all regression equations the effect of process temperature was found to be insignificant. Finally, the consumer-optimized composition of the fat and the added SCN can be used to formulate a marketable product.

Modelling of Batch Lactic Acid Fermentation in the Presence of Anionic Clay

“…Accordingly, an increase in gel viscosity and strength was observed at larger values of milk total solid content as well as a grainy texture and signifi cant syneresis at a high milk mineral ma er content (1,20). During conventional heat treatment of milk, an increase in gel viscosity and strength, a decrease in whey separation and faster gelation were reported at higher temperatures, i.e.…”

“…Standardization stage involves an adjustment of milk total solid (fat, proteins, lactose and mineral ma er) content, whereas milk homogenization consists of fat globule disruption into smaller ones (1,(19)(20)(21). Conventional heat treatment of standardized and homogenized milk can be conducted at 80-85 °C for 30 min or at 90-95 °C for 5-10 min (1,2,19).…”

“…bulgaricus (L. bulgaricus) is used in yoghurt production (1,2,(19)(20)(21)(22)(23)(24). A ratio of bacterial species of 1:1 and inoculation rates of 0.5-4 % (by mass) are recommended in order to obtain an optimal cell growth and good yoghurt properties (1,22,24).…”

“…Both species are thermophilic (S. thermophilus bacterium exhibits an optimal growth at 39 °C, L. bulgaricus at 45 °C, and mixed culture at 42-43 °C) and can convert homofermentatively the lactose into LA as a main product (1). Besides LA, the LAB yield low amounts of acetaldehyde, diacetyl, acetone, acetic acid, formic acid and other compounds contributing to characteristic yoghurt fl avour (1,(20)(21)(22)(23). From a physiological point of view, the fermentation process consists of two stages.…”

“…Lower incubation temperatures (38-40 °C) lead to a lower cell growth rate, longer fermentation time and highly cross-linked protein network with small pores, yielding an increase in gel viscosity, strength and creaminess (smoothness) along with a decrease in whey separation (1,19). Final pH values between 4.1 and 4.7 are recommended in order to achieve appropriate cell growth and a good gel quality (1,2,(19)(20)(21)(22). A higher value of the fi nal pH (4.6-4.7), implying a shorter fermentation time, conduces to a less fi rm and viscous gel having a higher concentration of viable LAB and a more pronounced whey separation in comparison with a lower pH value (4.1-4.2) (1).…”