No abstract

Characteristics and properties of 4 Thai purple sweet potato flours, Maejo 343, Phichit 65-3, Phichit 290-9 and Torperk were determined in terms of native and pre-gelatinized flours. Color, physicochemical properties and antioxidant activity of native and pre-gelatinized flours depend on their varieties. All native flours showed low redness (a*) and blueness (-b*) values but high pasting properties. Pre-gelatinized flours had a unique purple color and high antioxidant activity. Flours produced by Phichit 65-3 showed a deep intense purple color, high anthocyanins and good antioxidant activity. Both native and pre-gelatinized Phichit 65-3 flours were used as the main raw materials of air-puffed pre-gelatinized flours with different ratios at 10%, 30% and 50%. Increasing the content of pre-gelatinized flours improved color, expansion and antioxidant activity of snacks. Low hardness (9.55-11.65 kg) was presented in all snacks prepared from sweet potato flours. Purple sweet potato snacks prepared from 50% pre-gelatinized flour had good appearance, light texture, high anthocyanins and high antioxidant activity. Results showed that Thai purple sweet potato flours can be used to produce healthy snacks with improved appearance and texture. They also have potential as sources of natural colorants and antioxidants in food products.

Sweet glutinous rice products or khao-mak in Thai were prepared by fermenting cooked glutinous rice (RD6 variety) using traditional starter cultures from Samut Sakhon (SSK) and Pathum Thani (PTT) Provinces at room temperature (28±2 °C) for 3 days. Amylolytic activities of microbial excisting in the traditional starter cultures were tested. Meanwhile, types and amounts of microbial growth in fermented rice products were investigated. Both traditional dried starter cultures showed strong amylolytic activity after inoculation for 2 and 3 days in starch agar. Microbiological profiles of rice fermentation were varied in total plate count, yeast and molds over the fermentation period. Different starter cultures resulted in a wide variation of end products with diverse chemical, microbiological and morphology properties; however those changes exhibited similar trends in all treatments. As fermentation time increased, protein content remained unchanged while total soluble solids, pH, acidity, sugar and alcohol content markedly increased compared with unfermented cooked rice. PTT showed products with higher acidity and alcohol content (0.50%, 2.58%) than SSK (0.31%, 1.85%). Morphological examination of rice grains revealed that microbial growth started from the outer surface and then moved inside the rice grains with greater corrosion was observed as fermentation time increased. Pasting and gelatinization properties of the rice flour were also strongly affected by fermentation.