Ten different foods containing local Thai vegetables were selected to study their antioxidant and antimutagenic properties. The antioxidant capacity, antimutagenicity, and total phenolic content of methanol extracts obtained from cooked food samples exhibited a wide variation ranging from 24-140 mg vitamin C equivalent/100 g, 53-93% and 35-125 mg gallic acid equivalent/100 g. The three foods highest in antioxidant capacity were Kaeng Hoi Bai Chaplu (wild betal curry), Phat Sator (stir-fried petai beans), and Kaeng Pa Gai (mixed vegetables curry). The foods that exhibited an antimutagenicity greater than 85% were Tomkathi Saibua (water lily stalk curry), Kaeng Pa Gai, Kaeng Taipla (southern curry), and Kaeng Lueang Khun (giant taro stem curry). Next, aiming to develop retort pouch food products, the effect of sterilization heat (121°C) on four selected foods was studied. Antioxidant capacity, antimutagenicity, and total phenolic content increased by 0-120%, 13-40%, and 6-54% after sterilization, respectively.
Flour and starch were prepared from six Thai banana cultivars: Kluai Hom, Kluai Khai, Kluai Lebmuenang, Kluai Namwa, Kluai Hakmuk and Kluai Hin, and their resistant starch (RS), in vitro starch digestibility and physico-chemical properties were determined. The RS content of the flour is 52.2-68.1%, with flour from Kluai Hin containing the highest amount of RS, followed by that from Kluai Hakmuk. The starch has a higher RS content (70.1-79.2%), the highest value coming from Kluai Hakmuk starch, followed by Kluai Hom starch. A significant linear relationship between apparent amylose and RS was observed. Interestingly, most of the flour showed a slower rate of in vitro starch digestibility than that of the starch, with Kluai Hin flour exhibiting the slowest rate, followed by Kluai Namwa. Rapid viscosity analysis showed significantly higher peak viscosity of the starch than the flour, the highest final and setback viscosity being obtained from Kluai Hin starch. Differential scanning calorimetry showed an endothermic transition enthalpy over a range of 17.4 J/g for Kluai Lebmuenang starch to 18.6 J/g for Kluai Hin starch. X-ray diffractograms of the starches exhibited a typical B-pattern with Kluai Hin showing the highest degree of relative crystallinity (31.3%) with a sharp peak at 5.5. The overall results seemed to indicate an effect of the BB genotype on the resistance of banana starch granules to enzymatic digestion due to amylose molecules and the crystallinity of amylopectin.
Samples from 29 starchy foods and 11 cultivars of banana were analyzed for their contents of resistant starch (RS), digestible starch and total starch, as well as the in vitro starch digestibility. The RS analysis was based on a-amylase and amyloglucosidase hydrolysis followed by colorimetric assay of the glucose released. The results showed that the main RS sources were found in the legume group (10.3 ± 1.2% to 22.9 ± 0.0%), glass noodle products (9.1 ± 0.8% to 11.3 ± 1.5%) and bananas (52.2 ± 4.1% to 61.4 ± 2.3%). For the rice group, the effect of processing methods on the retrograded RS formation was investigated. Khanomjean produced with fermentation had a higher RS content (8.5 ± 1.1%) than that of the cooked white rice of the high-amylose cultivar. With the rice snacks, the process for puffing kaotung and kaokreupvor by frying and roasting produced a higher RS content (2.6 ± 0.0% and 2.9 ± 0.3%, respectively) than in the raw samples. Among the rice noodles, vermicelli contained a higher RS content than the others. Moreover, a gelatinization effect on the RS contents was clearly evident, with the gelatinized cassava starch (2.2 ± 0.0%) having a lower RS content than the commercial starch (44.6 ± 0.3%), whereas the commercial RS content was high (58.5%). Finally, the test on in vitro starch digestibility showed that the legume samples, particularly with red beans, had the lowest rate of starch digestibility compared to the other samples.
ABSTRACT Frozen food products are gaining acceptance in Thai food industry and frozen bualoy dessert is a good opportunity for marketing in domestic and for exports. One important factor affecting quality of frozen starchy foods is retrogradation of starch gels. Thus freeze‐thaw stability of a frozen bualoy made from total waxy rice flour was studied and compared among the samples modified by 20 and 30% cross‐linked tapioca starch (CTS) derivatized with phosphorylation and 0.25% propylene glycol alginate (PGA). The waxy rice flour was pregelatinized by adding boiled water before shaping as a ball, then boiled and mixed with coconut syrup. All samples were subjected to five freeze‐thaw cycles over 60 days in a conventional freezer (–18°C). Texture analysis firmness and stickiness of the nonfrozen gels substituted with 20% CTS (382 ± 43, 20.5 ± 7.1 g·f) and 30% CTS (493 ± 37, 31.1 ± 7.0 g·f) were significantly different as compared with the control (329 ± 22, 14.8 ± 3.1 g·f). Similar results were observed for the samples continuously frozen for 60 days. The effects of freeze‐thaw stability to the frozen gels of the control, CTS, and PGA substituted samples appeared after two cycles and exhibited a large increase in firmness and stickiness at the fourth cycle. The firmness values obtained from the control and the samples substituted with 20% and 30% CTS were 2,397 ± 197, 2,182 ± 203, and 2,104 ± 200 g·f, respectively. This evidence was also observed with the samples containing PGA, but the effect was slightly less. This might account for the recrystallization of amylopectin molecules induced by freeze‐thawings. With DSC, the waxy rice gels showed a significant increase in the melting enthalpy (2.39 ± 0.23 J/g) at the fifth cycle from the nonfrozen gels (0.11 ± 0.02 J/g). The sensory tests of the bualoy s were correlated with textural qualities that were acceptable to the panelists when the freeze‐thawing went no further than the second cycle.
