THE PRODUCTION OF A FUNCTIONAL YOGURT FORTIFIED WITH BROWN RICE

Abstract

In this study, functional yogurt with high γ-aminobutyric acid (GABA) content was produced by using crude extracts of germinated brown rice (GBR). GABA fortification by GBR is considered as easy, applicable and economical process for the development of functional yogurt. Germination was achieved for 96 hours and rice was dried and grounded after germination. Effect of germination period on GABA production, total γ-oryzanol content and total antioxidant capacity was investigated for GBR. It was observed that GABA amount significantly increased with germination period and reached to almost 14 folds after 84 hours of germination. However, γ-oryzanol did not change significantly with germination. The total antioxidant capacity of GBR decreased in first 12 hours of germination then increased up to 84 hours with minor differences (p < 0.05). GABA fortified functional yogurt samples at different levels were prepared and manufacturing conditions were optimized by using crude extracts obtained from 84 hours GBR flour. And these crude extracts having GABA contents of 13.88 ± 0.71 and 26.86 ± 0.34 mg/100 g dry matter were prepared from 20 and 40 g of flour samples, respectively. The effect of storage period and the addition of GABA standard or crude GBR extracts in all samples were determined by the comparison to control yogurt sample. On the other hand, naturally occurring GABA was not detected in control yogurt (CTR-Y). Fermentation process results in GABA reduction of about 10.36, 14.39 and 18.57% in yogurt samples with GABA standard (CTR-G), crude extracts of 20 g GBR (GBR20) and crude extract of 40 g GBR (GBR40), respectively (p < 0.05). Whereas, storage period (21 days) has no significant effect on the GABA content of fortified yogurt samples (GABA content of CTR-G, GBR20 and GBR40 yogurt samples is 9.24 ± 0.07, 10.84 ± 0.14 and 21.78 ± 0.13 mg/100 g fresh yogurt, respectively). As compared to CTR-Y yogurt, water holding capacity (WHC) and textural parameters (hardness and gumminess) significantly decreased in GABA containing yogurt samples after 21 days of storage. However, during initial 14 days of storage, WHC and texture were first increased in all yogurt samples and then the reduction was observed during rest of the storage. In contrast, parameters such as cohesiveness and springiness were improved non-significantly for GABA enriched yogurt samples. Total antioxidant capacities of yogurt samples were increased with GABA fortification in the form of crude extracts but yogurt enriched with standard GABA has been observed with lower antioxidant capacity as compared to control yogurt (p < 0.05), whereas storage period has a non-significant effect on the antioxidant capacity of all yogurt samples. The results of sensory evaluation revealed less acceptability for GBR40 yogurt than control yogurt but GBR20 has been selected as a suitable replacement for conventional yogurt. Furthermore, only a single portion of GBR20 yogurt is enough to supply more than 10 mg of GABA, which is enough for the treatment of individuals with mild hypertension according to the related literature.