Abstract
The effect of cooking on starch hydrolysis, polyphenol contents, and in vitro α-amylase inhibitory properties of mushrooms (two varieties Russula virescens and Auricularia auricula-judae), sweet potato (Ipomea batatas), and potato (Solanum tuberosum) was investigated. The total, resistant, and digestible starch contents of the raw and cooked food samples (FS) ranged from 6.4 to 64.9; 0 to 10.1; and 6.4 to 62.7 g/100 g, respectively, while their percentages of starch digestibility (DS values expressed as percentages of total starch hydrolyzed) ranged from 45.99 to 100. Raw and boiled unpeeled potato, raw and boiled peeled potato, raw A. auricula-judae, and sweet potato showed mild to high α-amylase inhibition (over a range of concentration of 10–50 mg/mL), which was lower than that of acarbose (that had 69% inhibition of α-amylase over a range of concentration of 2–10 mg/mL), unlike raw R. virescens, boiled A. auricula-judae, and boiled sweet potatoes that activated α-amylase and boiled R. virescens that gave 0% inhibition. The FS contained flavonoids and phenols in addition. The significant negative correlation (r = −0.55; P = 0.05) between the α-amylase inhibitory properties of the raw and cooked FS versus their SD indicates that the α-amylase inhibitors in these FS also influenced the digestibility of their starches. In addition, the significant positive correlation between the α-amylase inhibitory properties of the raw and cooked FS versus their resistant starch (RS) (r = 0.59; P = 0.01) contents indicates that the RS constituents of these FS contributed to their α-amylase inhibitory properties. The study showed the usefulness of boiled unpeeled potato, boiled potato peeled, and raw sweet potato as functional foods for people with type 2 diabetes.
Highlights
One of the therapeutic approaches that have been found to be useful in the management of type 2 diabetes is reduction of postprandial hyperglycemia through inhibition of the carbohydrate hydrolyzing enzymes, such as α-amylase in the digestive tract [1]
Whereas resistant starch (RS) was not detected in boiled sweet potato and the raw forms of R. virescens and A. auricula-judae, boiling of R. virescens, A. auricula-judae, and peeled potato resulted in significant increase (P < 0.05) of RS compared with their raw
Since sweet potatoes are eaten in the raw form in Nigeria, the findings of this study reveals that consumption of the raw form of unpeeled potato will be of more benefit to people with type 2 diabetes than consumption of the boiled unpeeled form, raw and boiled peeled forms, respectively
Summary
One of the therapeutic approaches that have been found to be useful in the management of type 2 diabetes is reduction of postprandial hyperglycemia through inhibition of the carbohydrate hydrolyzing enzymes, such as α-amylase in the digestive tract [1] Synthetic drugs such as acarbose and others that are currently being used to inhibit these enzymes, tend to be non-specific in targeting different glycosidases, thereby producing adverse effects. Several factors influence the digestibility of starches in foods such as: carbohydrate contents of foods, nutritional composition of starch [rapidly digestible starch, slowly digestible starch, and resistant starch (RS)], method of cooking foods, and others These factors tend to affect the change in blood glucose after eating a meal [4]
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