Abstract
The aim of this study was to investigate the effect of preparation method and particle size on digestion of starch in fresh and dry pasta types. Pasta samples were boiled, refrigerated and re-heated, with samples collected after each stage, and then prepared as small (2 mm) and large (5 mm) particles for subsequent starch digestibility testing and logarithm of slope analyses. There were significant main effects of particle size (F1,24 = 568.895, p < 0.001, ηp2 = 0.960) and processing treatment (F2,24 = 19.897, p < 0.001 ηp2 = 0.624) on starch digestibility overall, however the main effect of pasta type was not significant at the p < 0.05 level (F1,24 = 2.978, p = 0.097, ηp2 = 0.110). Particle size had the largest effect on digestibility, and the extent of starch digestion was at least 50% lower in samples prepared as large particles compared with small particles. The most digestible sample was the boiled fresh-type pasta prepared as small particles (C∞ = 57.9%) and cold storage alone and/or with subsequent re-heating significantly reduced the extent of digestion in this sample to ∼40.6%. In the dry pasta type, processing treatment had no significant effects on starch digestibility. The rate constant, k, was not significantly altered by processing treatment or pasta type (k = 0.0275 min-1, mean of all samples). These findings suggest that cold-storage and re-heating treatments have limited potential to impact on glycaemic responses and highlight the importance of masticated particle size as a potential rate-limiting factor in digestibility studies.
Highlights
Starch-rich foods that evoke a high glycaemic response are modifiable risk factors for obesity, type 2 diabetes and cardiovascular disease and there is a need to promote staple foods that attenuate postprandial blood glucose responses.[1,2,3] Pasta is a widely consumed food product typically prepared from extrusion of wheat-based dough and is available either as a ‘fresh type’ where egg is included in the dough, or as a ‘dry-type’, in which extruded pasta shapes are dried at high temperature
Larger sections cut to a length of ∼5 mm from dry pasta were cylindrical, whereas the larger sections cut from fresh pasta had a somewhat flattened appearance
The measured amount of starch digestion products increased over time for all samples and the resulting starch digestibility curves obtained from large particles were essentially linear over the 90 min time-course, whereas curves obtained from small particles were first-order
Summary
Starch-rich foods that evoke a high glycaemic response are modifiable risk factors for obesity, type 2 diabetes and cardiovascular disease and there is a need to promote staple foods that attenuate postprandial blood glucose responses.[1,2,3] Pasta is a widely consumed food product typically prepared from extrusion of wheat-based dough and is available either as a ‘fresh type’ ( pasta fresca) where egg is included in the dough, or as a ‘dry-type’ ( pasta secca), in which extruded pasta shapes are dried at high temperature. The susceptibility of starch to amylolysis during digestion regulates the availability of glucose for absorption and is known to have a major impact on the postprandial glycaemic response to carbohydrate foods. Starch digestibility has been shown to occur more slowly in pasta than in other high glycaemic carbohydrate foods,[6,7] but it is unclear if the low digestibility is due to intrinsic properties of the starch or the properties of the surrounding food matrix. The gluten protein network has been shown to delay the activity of α-amylase on starch during in vitro digestion,[7,8,9] and the type and amount of protein may impact on texture and glycaemic responses. Amylose and amylopectin, the α-glucan polymers of starch, are known to undergo structural changes when exposed to different processing conditions, with implications for its susceptibility to amylolysis.[10,11,12,13] For instance, refrigeration of gelatinised starch is known to promote the formation of retrograded starch, in which the re-association between α-glucan chains of amylose and eventually amylopectin reduces its susceptibility to amylolysis.[11,12] On a macroscopic level, the surface area to volume ratio of food macroparticles that are swallowed are recognised to impact on metabolic responses.[14,15] Mastication
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