Influence of heat treatment on physicochemical and rheological characteristics of natural yogurts

Abstract

The aim of this study was to assess the influence of heat treatment on physicochemical and rheological characteristics of natural yogurts, as well as the influence of lyophilization process on natural yogurts after reconstitution. In the first experiment, three yogurt treatments were processed, as follows: Treatment 1, yogurt produced with raw refrigerated milk; Treatment 2, yogurt produced with refrigerated pasteurized milk; and Treatment 3, yogurt produced with UHT (ultra-high temperature) milk, in addition to analyses of fat, protein, moisture, titratable acidity, and pH. The shelf life of yogurts at 1, 8, 15, 22, and 29 days of storage, as well as pH, acidity, syneresis, viscosity, viable lactic bacteria, and total coliforms were also assessed. In the second experiment, yogurts were submitted to lyophilization process, performed by scanning electron microscopy analysis and subsequently in those reconstituted, in addition to being assessed the physicochemical, rheological, and viable lactic bacteria characteristics. The results found in the first experiment showed that heat treatment was positive for viscosity, syneresis, and lactic bacteria, being viable until the 15th day of storage only for yogurts submitted to heat treatment. In the second experiment, lyophilization preserved the physicochemical characteristics of yogurts, but the number of initial lactic bacteria was different, also negatively affecting yogurt viscosity. Key words: Acidity. Viable lactic cells. Lyophilization. pH. Shelf life. ResumoObjetivou-se avaliar a influência do tratamento térmico nas características físico-químicas e reológicas de iogurtes naturais e a influência do processo de liofilização em iogurtes naturais após sua reconstituição. No primeiro experimento, foram processados três tratamentos de iogurtes Tratamento 1 -iogurte produzido com leite cru refrigerado; Tratamento 2 -iogurte produzido com leite pasteurizado refrigerado; Tratamento 3 -iogurte produzido com leite UAT (Ultra Alta Temperatura) e feitas as análises de gordura, proteína, umidade, acidez titulável e pH. Avaliou-se também a vida de prateleira dos iogurtes nos tempos 1, 8, 15, 22 e 29 dias de armazenamento, tendo sido feitas as análises de pH, acidez, sinérese, viscosidade, bactérias lácticas viáveis e coliformes totais. No experimento II, os iogurtes foram submetidos ao processo de liofilização realizado analise de microscopia eletrônica de varredura

Effect of milk types on the attributes of a glutinous rice wine-fermented yogurt-like product

“…The physicochemical properties of milk can be greatly affected by the thermal sterilization parameters of raw milk. Célia et al (2017) reported that the highest protein content was found in yogurt produced by pasteurized milk compared with UHT and raw refrigerated milk, which is agreement with our study. Because skim milk powder was added to S milk, the protein content of the S KWL was higher than H KWL.…”

“…The fat content in the dairy products is reported to be related to the lipolysis of fungi, especially Saccharomyces, which also was detected in the finished products of H KWL. Further, the difference of pH value was not significant in all samples, which was similar to a previous study (Célia et al, 2017).…”

Probiotic Potential and Technological Properties of Bacteriocinogenic Lactococcus lactis Subsp. Lactis UTNGt28 from a Native Amazonian Fruit as a Yogurt Starter Culture

“…The fat content registered in this research reduced considerably in the yogurt formulations with a lower pH after the fermentation, while minor changes were registered in the protein content, indicating that no degradation was evident after fermentation (Table 4). Previous research indicated a reduction in both fat and protein content in the final product after fermentation [39]. Based on our results, the fat decreased in all formulations depended on the bacterial combinations used in the fermentation process.…”