Influence of sterilization, drying and oat bran enrichment of pasta on glucose and insulin responses in healthy subjects and on the rate and extent of in vitro starch digestion.

The effects of sterilization and oat bran enrichment of pasta on the glucose and insulin responses in healthy subjects were evaluated. Cooked and canned spaghetti and cooked fettucini without and with enrichment with oat bran (28%) were compared. Further, the effects of various low- and high-temperature drying conditions for spaghetti, cooking time and sterilization on the starch digestion rate and content of enzyme-resistant starch (RS) in vitro were also studied. Various cooking quality data were also determined to allow interpretation of results. The incremental glucose area (0-120 min) produced by canned spaghetti was twice the area of that produced by cooked spaghetti (69.03 vs 35.45 mmol/l x min, P less than 0.01). The incremental insulin area (0-120 min) was also significantly higher with canned spaghetti (17,500 vs 12,600 pmol/l x min, P less than 0.05). The rapid digestion was caused by excessive swelling of starch during sterilization that promoted a very soft texture of the spaghetti. Enrichment of fettucini with oat bran reduced slightly the incremental insulin area (15,600 vs 20,100 pmol/l x min, P less than 0.05, for 0-120 min), but did not significantly reduce the glucose area. Drying conditions and cooking times could be varied within broad limits without affecting the rate of starch digestion in vitro of cooked spaghetti. In sterilized spaghetti the content of resistant starch was higher than that found in cooked 'al dente' spaghetti (2.2-3.4 vs 0.5 mg/100 mg total starch). In conclusion, sterilization influences the nutritional properties of starch in pasta by substantially increasing the glucose and insulin responses and by formation of resistant starch. The effect of oatbran environment is restricted mainly to a slight decrease in the insulin response.