Secagem de iogurte por atomização ou liofilização: efeitos sobre viabilidade microbiana e características físicas, químicas e sensoriais

Abstract

Yogurt is the most consumed fermented milk in the world, recognized for its nutritional value and beneficial effect to health. However, its shelf life is relatively short compared to other dairy products. In this context, dehydration arises as an alternative for conservation, reduction of costs with storage and transportation, as well as diversification of the product niche. Therefore, the present work aims to develop yogurt powder by freeze drying or spray drying, within the parameters pre-established by Brazilian legislation for fermented milk. Formulations were prepared with lecithin (0.2, 0.4 and 0.6%), gum arabic (0.2, 0.4 and 0.6 %) and maltodextrin (5, 10 and 15 %). We performed the tests according to a central composite rotatable design (CCRD) 2n, with n = 3 as the number of independent variables and 3 central points. We also performed analyses of solubility, colorimetry (luminosity) and microbiological analyses of Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus salivarius subsp. thermophilus counts as response variables. Afterwards, 2 freeze dried samples, L1 (without additives) and L2 (with additives 15 % of maltodextrin and 0.6 % of gum arabic) and 2 spray dried ones, A1 (without additives) and A2 (with additives 15 % of maltodextrin and 0.6 % of gum arabic), were characterized by some analyses, such as: physical (wettability, solubility,sorption isotherms, rheological and colorimetry and Aw) centesimal composition, fatty acid profile, acetaldehyde content, electrophoretic profile of proteins and microbiological counting of lactic acid bacteria, after processing and during storage in cooling and ambient temperatures. In addition, sensory analysis on the acceptance and characterization of rehydrated yogurt samples using a 9-point hedonic scale and the Check All That Apply (CATA) methodology were also performed. The additives positively influenced the preservation of Lactobacillus delbrueckii subsp. bulgaricus cells during the dehydration process, while maltodextrin and lecithin collaborated to decrease Streptococcus salivarius subsp. thermophilus cells. The sorption parameters of the yogurt powder samples were better adjusted to the Gugghenheim, Anderson and BOER (GAB) model. The rheological data of the rehydrated samples were adjusted to the Ostwald-de-Waele and Herschel-Bulkley models. The samples processed showed less acceptance than the natural and commercial samples. However, the freeze dried samples presented good acceptance. They were characterized as creamy, homogeneous and with characteristic yogurt flavor. The spray dried samples showed low acceptance. They were characterized as yellowish, buttery, fatty, creamy and homogeneous. Both the freeze dried and spray dried samples were in compliance with the standards required by Brazilian legislation, but the freeze drying process was shown to be more efficient, both in the preservation of lactic acid bacteria and in the retention of acetaldehyde, the main aromatic compound of yogurt. Spray drying and freeze drying preserved the viability of lactic acid bacteria above that recommended by the Brazilian legislation for more than 150 days when stored at 6 ºC. When stored at 30 °C, the bacterial viability was 45 days for spray dried samples and 75 days for freeze dried ones. All samples showed viability of lactic acid bacteria for storage times much longer than the traditional yogurt, which confirms that both drying methods are efficient for yogurt preservation.