Assessment of bioactive compounds and their in vitro bioaccessibility in whole-wheat flour pasta

Highlights

• Pasta processing produce changes in polyphenol profile and in their antioxidant properties.

• Cooking step is important to increase the release of bounded polyphenols.

• Only a small fraction of starting polyphenols can be absorbed in the small intestine.

• This is the first report on the bioaccessibility of five new wheat polyphenols.

Abstract

We studied the polyphenol profile and antioxidant properties of cooked whole-wheat pasta to evaluate its effective antioxidant capacity, including changes produced by its production and in vitro digestion. The polyphenol profile was studied by HPLC–ESI-MS/MS, while the antioxidant capacity was measured by TEAC and FRAP assays. Results show that the polyphenol profile and antioxidant capacity change along the elaboration of cooked pasta, being the cooking step important to increase the release of bound polyphenols, enhancing their antioxidant properties. On the other hand, the study of the bioaccessibility of polyphenols, using an experimental model that simulates human gastrointestinal digestion and subsequent absorption, showed that only a small fraction of the starting polyphenolic compounds, mainly free polyphenols, could be absorbed by the small intestine; thus, reducing their effective antioxidant capacity. To our knowledge, this is the first report showing the bioaccessibility of hydroxybenzoic acid glucoside, hydroxybenzoic acid diglucoside, tryptophan, 6-C-glucosyl-8-C-arabinosyl-apigenin and diferulic acids.

Introduction

In the last decades, there has been a growing interest in enhancing the quality and nutritional value of foods to achieve the maximum benefits of the diet. In this context, the nature of the ingredients from which food is made, the different processing stages as well as the effect of cooking on the conservation of food nutrients and bioactive compounds are of great relevance.

Being distributed and consumed worldwide, pasta is an important component of the daily diet, because it can be made from different cereals, and fortified with different nutrients, bringing reasonable nutritional advantages to different populations (Yadav & Gupta, 2015).

Among the bioactive compounds that are important to be evaluated in food, polyphenols stand out. These compounds have shown beneficial effects on human health due to their proposed antioxidant action. However, recent studies have shown that technological processes can affect both the profile and the antioxidant properties of polyphenols contained in food (Verardo et al., 2011, Fares et al., 2008, Fares et al., 2010, Zielinski et al., 2001, Li et al., 2015, Yu and Beta, 2015, Lu et al., 2014, Gélinas and McKinnon, 2006). Moreover, some processes can decrease the polyphenol content (Fares et al., 2008), while others increase it, due to a greater availability of these bioactive compounds in food (Fares et al., 2010, Zielinski et al., 2001, Yu and Beta, 2015, Lu et al., 2014, Gélinas and McKinnon, 2006). Thus, the study of changes in the polyphenol profile, as a consequence of food technology, is important to understand the changes observed in the antioxidant properties, contributing to the development of processing methods that help to maintain or increase the antioxidant capacity of foods.

In the same context, polyphenols must be bioavailable to perform their antioxidant action (Manach, Williamson, Morand, Scalbert, & Rémésy, 2005). The most abundant polyphenols are not always the main bioactive compounds in the organism. Low bioactivity can be associated with a lower intrinsic activity, low absorption in the intestine, quick metabolism, or rapid excretion (Manach, Scalbert, Morand, Rémésy, & Jiménez, 2004). Some polyphenols are relatively poorly absorbed in the intestine (their absorption ranges from 0.3% to 43%), so the concentration of their metabolites in plasma may be very low (Manach et al., 2005). Non-absorbed polyphenols, mainly those that form esters, glycosides or polymers, can reach the colon, where they can be fermented by the colonic microflora, generating metabolites which are colon-absorbed, appearing as conjugated derivatives in the plasma, and being further distributed to organs and tissues (D’Archivio, Filesi, Varì, Scazzocchio, & Masella, 2010). Once polyphenols are absorbed and metabolized, they may return to the duodenum through the enterohepatic circulation, prolonging their presence in the organism, or they can be eliminated by urine (Manach et al., 2004).

Many factors may influence the bioavailability of a compound, including its bioaccessibility, absorption, distribution in tissues, and bioactivity (Mateo Anson et al., 2009, Domínguez-Avila et al., 2017). Thus, the first step to understand the bioavailability is to study the bioaccessibility. The bioaccessibility is the fraction of a compound that is released from the food matrix in the gastrointestinal lumen, and is thus available to be absorbed into the gastrointestinal tract (Saura-Calixto, Serrano, & Goñi, 2007). This absorption may be influenced by the chemical form and the solubility of the compound, the interaction with other food ingredients (food matrix), molecular transformations, different cellular transports, metabolism, and the interaction with the intestinal microbiota (Neilson & Ferruzzi, 2011). Only those polyphenols released from the food matrix by the action of digestive enzymes and the bacterial microflora (large intestine) are bioaccessible in the intestine, and therefore, potentially bioavailable to exert their effect (bioactivity) on the human organism.

Few reports have shown the bioaccessibility of antioxidant compounds in products made from wheat flour (Gawlik-Dziki et al., 2009, Mateo Anson et al., 2010). Some authors have found that digestion can increase the antioxidant capacity of cereals with respect to extracts of these cereals (Liyana-Pathirana and Shahidi, 2005, Nagah and Seal, 2005, Pérez-Jiménez and Saura-Calixto, 2005). Therefore, digestion appears to be an important factor to enhance the antioxidant capacity of cereals. These results are particularly important, since they suggest that antioxidants exert their effect on the digestive tract, providing an environment that protects the intestinal epithelium from pro-oxidant compounds.

Thus, the main goal of this study was to verify the effective antioxidant properties of whole-wheat pasta, evaluating changes in the polyphenol profile and antioxidant properties throughout the production, cooking and digestions steps. Thus, we looked to verify which of these antioxidant compounds was degraded during the cooking process, leading to changes in the effective antioxidant properties as a consequence of cooking. Additionally, we also evaluated the bioaccessibility of polyphenols arising from cooked whole-wheat pasta by an in vitro digestion model, including a final dialysis step to simulate intestinal absorption. We hypothesize that the polyphenol profile present in whole wheat will be modified by the pasta production, cooking and digestion, leading to a reduced effective antioxidant capacity compared to the starting materials, which must be considered in the dietary information.