Acidic milk beverage production by using glucono-delta-lactone

Acidic milk products are yoghurt-like or ayran-like products that are manufactured by using an acidification agent instead of starter culture. In the production of these products, milk is held at a certain temperature for required time for development of acidity as in fermentation. Acidic milk beverages can be produced by addition of water to the gel obtained after acidification or adding acidification agent to diluted milk depending on the process as in the production of ayran. Nowadays, acidic milk beverages are popular food products. They can be produced by addition of probiotics and prebiotics which renders them as functional products. In fact, fermented milk products are most commonly manufactured functional products. In addition, they can be produced by addition of fruits, fruit extracts and other functional ingredients. Functional food products increase the health benefits of the products for the consumers apart from their nutritional value. Consumers prefer functional food products due to their health benefits. This current trend direct food industry for production of functional food products such as acidic milk beverages. Glucono-delta-lakton (GDL) is a commonly used acidification agent. It is a food additive which is allowed for use in food products. GDL has been used in production of meat and yoghurt. In the manufacture of yoghurt and ayran, the aim of fermentation is to acidify milk by production of lactic acid from lactose by starter culture. In acidification by GDL, gluconic acid is formed from GDL depending on its concentration, temperature and time. Controllable acidification is obtained without relying on starter culture and fermentation by the use GDL. Production of fermented or acidified milk products is based on formation of an acid gel from milk. Formation of appropriate structure is important for quality and storage stability in these products. Serum separation, development of excessive sourness and microbial spoilage can occur during storage which reduce quality and shelf life of these products. The aim of this study was to determine usage potential of use of GDL for acidification instead of fermentation in production of acidified milk beverage. For this purpose, acidic milk beverages were prepared from pasteurized milk by using only starter culture, only GDL and starter-GDL combination. Milk was heated to 43C and then starter culture or GDL was added. The samples were held at this temperature until a pH of 4,6 was obtained. After decreasing pH of the samples to 4,6, pasteurized and cooled distilled water was added to the coagulum obtained at a ratio of 40%. Samples were homogenized and stored at refrigeration temperature. Physicochemical properties, sensory properties, water holding capacity, serum separation and total aerobic viable microorganisms and mold-yeast counts of the samples were determined during storage time. Titratable acidity of the samples was determined by titration with NaOH. Titratable acidity was expressed as percentage of lactic acid in the samples. Water holding capacity was measured by a centrifuge method where separated serum from the product was determined. Serum separation from the samples was determined by using graduated cylinder method. Total aerobic viable microorganisms were enumerated on using plate count agar by spread-plate method. Mold-yeast were enumarated on Dichloran Rose Bengal Chloramphenicol agar by spread-plate method. Sensory textural and flavor properties of the samples were measured by descriptive sensory analysis method by using a scale from 0 (none) to 7 (extremely high). Textural and appearance attributes including consistency, particulated structure, particle size, whiteness and lightness were evaluated. Flavor attributes consisted of ayran-like taste, sourness, creamy taste, foreign taste and foreign smell. In addition, overall impression of the samples was determined. pH values of the samples with only GDL and only starter culture were found to be similar. However, pH value of the sample produced with starter-GDL combination was found to be statistically different than those of the other samples. pH values of the samples with only starter and only GDL slightly decreased during storage while there was no change in the sample with starter-GDL combination. A similar trend as in pH was observed for titratable acidity of the samples. Titratable acidity of the sample with starter-GDL combination was found to be lower compared to those of the samples with only GDL or starter. While titratable acidity of the sample with starter-GDL combination was not changed, titratable acidity of the other samples increased after seven days of storage. Water holding capacity of the samples were found to be similar. Highest serum separation was observed in the sample with starter-GDL combination. Serum separation of the samples increased after seven days of storage. Effect of method of acidification on the counts of mold-yeast in the samples was not statistically significant. Numbers of mold-yeast increased and then decreased during storage time. While numbers of total aerobic viable microorganisms in the samples were similar at the beginning of the storage, the sample with starter culture was found to have the lowest number at the end of the storage time. The sample with starter culture had similar numbers of total aerobic viable microorganisms during storage time. On the other hand, the samples with GDL showed an increase in the numbers of total aerobic viable microorganisms at the seventh day of storage and then the numbers of microorganisms stayed constant. Sensory textural properties including consistency, particulated structure, particle size, whiteness and lightness of the samples were found to be similar. Textural properties of the acidic milk beverages were not affected by acidification method. On the other hand, flavor of the samples was significantly affected by acidification method. Ayran-like taste and sourness were found to be lower in the samples with GDL. Milk taste and smell were found to be dominating in the samples produced with only GDL. The sample with only GDL and the sample with starter-GDL combination were found to be similar in terms of their overall impression score. This study showed that GDL can be used for acidification in production of acidic milk beverages. However, it should be used together with starter culture for good flavor. Further studies are needed for evaluation of shelf life of the product.