This study determined vitamin D content in commonly consumed fish in Thailand and the effects of different cooking methods on vitamin D retention. Five species of freshwater fish and four species of marine fish were purchased from three representative markets. All of the fish were individually prepared according to common household practices. Vitamin D2 and D3 were determined using the HPLC standard method (AOAC method 995.05). The results indicated that vitamin D3 was the only detectable form of vitamin D in the fish. Vitamin D content of raw freshwater fish ranged from 2.42 to 48.5 µg per 100 g edible portion (EP), which was higher than that of raw marine fish (2.94 to 4.69 µg per 100 g EP). Common silver barb, Red Nile tilapia, and Nile tilapia (freshwater fish living in the limnetic zone) contained high levels of vitamin D (48.5 ± 26.5, 31.0 ± 7.7, and 19.8 ± 3.5 µg per 100 g EP, respectively). Boiled fish (except for Common silver barb), fried fish (except for Striped snakehead, Walking catfish, and Common silver barb), and grilled fish (except for Common silver barb, Giant sea perch, and Short-bodied mackerel) retained high levels of vitamin D, which were not significantly different (p > 0.05) from raw fish. Common silver barb, Red Nile tilapia, and Nile tilapia—cooked by boiling, frying, and grilling—are recommended for consumption as excellent sources of vitamin D.

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Organic acids had various health benefits such as citric acid can inhibit stone formation and break up beginning of small kidney stone. On the other hand, some organic acid showed negative health effects such as oxalic acid acts as anti-nutrients and can cause kidney stone. Most of Thai indigenous plants had sour taste; however general people believed that sour taste of plants could contain high ascorbic acid. In addition, there is limit report of organic acids and ascorbic acid in Thai indigenous plants. This study determined organic acids, ascorbic acid, pH, and total acidity in indigenous plants. Forty samples of 29 types of indigenous plants were analyzed. Results showed that young leaves of Cratoxylum formosum found the highest succinic acid (2454 ± 91 mg/100g fresh weight, FW) and high ascorbic acid (142 ± 35 mg/100g FW). Fruits of Antidesma ghaesembilla had high citric acid levels (5161 ± 109 mg/100g FW) but contained very low ascorbic acid (2 mg/100g FW). The sum of organic acids had significant and inverse correlations with pH (r = −0.680) and positive with total acidity (r = 0.672) but was not significantly correlated for ascorbic acid (r = 0.536). The sour taste of plants could derive from the sum of organic, citric, and formic acids, but not other organic and ascorbic acids. Against traditional belief, plants having a strong sour taste may not contain significantly high amounts of ascorbic acid.