Effect of raw material composition on glycaemic index of biscuit as a functional food

Abstract

Obzirom na porast svjesnosti o preventivnoj i protektivnoj ulozi prehrane kod mnogih oboljenja, u okviru ovog rada istraživane su mogućnosti razvoja keksa nižeg glikemijskog indeksa kao funkcionalnog proizvoda na bazi žitarica. Istraživanja su provedena na šesnaest vrsta laboratorijski pripremljenih keksa u kojima je suplementiran određeni udio bijelog pšeničnog brašna s integralnim žitaricama (zobeno i ječmeno brašno), integralnim pseudožitaricama (brašno heljde i amaranta), leguminozama (brašno rogača i soje) ili čistim prehrambenim vlaknima (zobena i jabučna vlakna). Preliminarna istraživanja bila su temelj za odabir najoptimalnijih receptura u koje je dodatno još uveden i inulin. Makronutritivne komponente (proteini, lipidi, dostupni ugljikohidrati, prehrambena vlakna) određene su standardnim analitičkim metodama, a in vitro probavljivost škroba kontroliranom enzimskom simulacijom gastrointestinalne digestije. U svrhu određivanja tehnološkog utjecaja (pečenja) na promatrane parametre, istraživanja su provedena i u uzorcima poluproizvoda (tijesta). Svim uzorcima keksa procijenjene su organoleptičke karakteristike iskazane ponderiranim bodovima. Glikemijski indeks (GI) završnih uzoraka keksa određen je sa zdravim dobrovoljcima oba spola i različite dobi. Rezultati kemijskih analiza pokazali su da je supstituiranjem integralnih žitarica, pseudožitarica i leguminoza moguće dobiti keks bolje makronutritivne kvalitete i protektivnih svojstava. Uvođenje čistih zobenih i jabučnih vlakana rezultiralo je povećanom protektivnom, ali smanjenom nutritivnom kvalitetom keksa, osobito obzirom na proteinsku komponentu. Očito je da čista prehrambena vlakna nisu sirovina izbora za kreiranje funkcionalnog keksa dobrih nutitivnih karakteristika. Smanjenjem udjela izomalta i lipidne komponente, te uvođenjem inulina smanjena je ukupna energijska vrijednost za 11.5%, te postignut gotovo optimalno uravnotežen izvor energije od pojedinih makronutrijenata. Uvođenje pseudožitarica i leguminoza rezultiralo je značajnim padom brzo dostupne glukoze (9.62-47.55%) i brzo probavljivog škroba (9.77-50.39%). Značajan porast udjela rezistentnog škroba postignut je uvođenjem pseudožitarica (43.32-55.94%). Utvrđeno je da pečenje značajno povećava probavljivost škroba i udio brzo dostupne glukoze. Provedene modifikacije rezultirale su povećanjem ukupne organoleptičke prihvatljivosti, u odnosu na referentni uzorak, kod svih istraživanih keksa osim uzorka s dodatkom brašna soje. Analiza rezultata pokazuje da niti jedan od istraživanih keksa nema visok glikemijski indeks. Referentni uzorak, uzorak s dodatkom šećera, te uzorci s heljdom i bez inulina imaju srednji GI (58.7-66.9), a s brašnom amaranta, soje ili rogača imaju nizak GI (44.9-52.5). Utvrđena je vrlo dobra korelacija između rezultata dobivenih in vitro metodom i vrijednosti GI koja ukazuje da je kreiranje keksa s nižim stupnjem probavljivosti škroba dobar pristup u snižavanju glikemijskog indeksa keksa, a time i povećanja njegovih funkcionalnih svojstava. Kao rezultat ovog istraživanja može se zaključiti da je uvođenjem odabranih sirovina moguće poboljšati nutritivni sastav, sniziti kalorijsku (energijsku) vrijednost, te sniziti glikemijski indeks, odnosno poboljšati funkcionalna svojstva keksa uz istodobno održavanje zadovoljavajućih organoleptičkih svojstava.Considering the increasing awareness of preventive and protective role of diet in many diseases, in the framework of this work, the possibilities of developing biscuits with lower glycaemic index as functional cereal-based products were investigated. Sixteen types of laboratory prepared biscuits were investigated, where a certain proportion of white wheat flour in the recipe was substituted with whole grain cereals (oat- and barley flour), whole grain pseudocereals (buckwheat- and amaranth flour), legumes (soy- and carob flour) or pure fibre (oat- and apple fibre). Preliminary investigations were the basis for selecting the most optimal formulation that was additionally supplemented with inulin. Macronutritive components (proteins, lipids, available carbohydrates, dietary fibre) were determined by standard methods of analysis, and in vitro digestibility of starch was determined by controlled enzymatic simulation of gastrointestinal digestion. To determine the impact of technological process (baking) on the observed parameters, investigations have been conducted in dough as well. All biscuits were conducted to organoleptic analysis and obtained results were presented by the weighted score. The glycaemic index (GI) of the final samples of biscuits was determined with healthy volunteers of both sexes and different ages. Results of the chemical analysis showed that by substitution of whole grain cereals, pseudocereals and legumes, it is possible to achieve a better macronutritive quality and protective characteristics of biscuit. Introducing pure oat and apple fibre resulted in increased protective, but decreased nutritional quality of biscuits, especially regarding protein component. It is obvious that pure dietary fibre are not raw materials of choice for creating functional biscuits with good nutritive characteristics. Reduction of isomalt content and lipid component and the introduction of inulin reduced the total energy value for 11.5%, and resulting in formulation with nearly optimally balanced energy source of each macronutrient. Introducing pseudocereals and legumes resulted in a significant decline of rapidly available glucose (9.62-47.55%), and rapidly digestible starch (9.77-50.39%). Significant increase of resistant starch content was achieved by pseudocereals implementation (43.32-55.94%). It was found that baking significantly increased the digestibility of starch and rapidly available glucose. Performed modifications resulted in an increase of overall organoleptic acceptability in all investigated samples, compared to the reference sample, except in biscuit supplemented with soy flour. The results show that none of the investigated biscuits had high glycaemic index. Reference sample, a sample with added sugar, and samples with buckwheat and without inulin had medium GI (58.7-66.9), while samples with amaranth-, soy- or carob flour had a low GI (44.9-52.5). A very good correlation between the results obtained by in vitro method and obtained GI values was determined indicating that the formulation of biscuits with lower starch digestibility represents good approach in lowering glycemic index of biscuits, and increasing its functional properties. As a result of this investigation it can be concluded that the introduction of selected raw materials to standard biscuit recipe can improve the nutritive composition, lower caloric (energy) value, lower the glycaemic index, and respectively improve the functional properties of biscuits while maintaining satisfactory organoleptic properties