Chemical characterization and biological effects of immature durum wheat in rats

Abstract

A durum wheat cultivar, Simeto, was grown in experimental fields and samples were collected at various stages of development (from 9 to 45 days after flowering) to assess changes in chemical composition during maturation. Fructans, in particular low molecular weight fructo-oligosaccharides, accumulated in the first 2–3 weeks after anthesis. The cultivar was then grown in an open field and collected at 15 days after anthesis and at maturity 45 days after anthesis. Experimental diets containing 53% wholemeal from immature or mature wheat, were fed for 6 and 12 weeks to two groups of growing rats. Glutathione, vitamins C and E and total hydrophilic or lipophilic antioxidant concentrations were determined in mature and immature wholemeal. The effects of feeding immature and mature wheat diets for the two experimental periods on the immune system, antioxidant status and plasma lipids were studied. Feeding immature wheat increased the proliferation rates of lymphocytes, indicating a stimulating effect on the immune response, decreased the plasma triglycerides and cholesterol levels, indicating a positive effect on lipid profiles. Antioxidant concentrations in blood and lymphocytes did not change significantly.

Introduction

Cereals have always been considered chiefly as dietary energy sources because of their high content of hydrolysable polysaccharides, but recently they have received attention as sources of compounds with added health benefits, these include fructose polymers (fructans and fructo-oligosaccharides) and antioxidant molecules such as glutathione, ascorbic acid, tocopherols, carotenoids and flavonoids (Adom et al., 2003, D'Egidio et al., 1997). Fructans are polymers consisting of chain of (2→6)-β-fructofuranosyl units sometimes branched through (2→1)-linkages, with a degree of polymerization (DP) from 3 to 60 substituting a sucrose molecule linked to the fructose residue of the disaccharide sucrose. Fructo-oligosaccharides (FOS), with an average DP 4–5 can be also produced from fructans by controlled chemical or enzymatic hydrolysis (Hendry and Wallace, 1993, Roberfroid et al., 1998). The concentration of fructans and antioxidant compounds in wheat grains depends on their phase of maturity, being significantly higher in the first period of ripening, and rapidly decreasing 2–3 weeks after anthesis (Paradiso et al., 2003). In a green-harvested wheat (cv. Freekeh), Humphries and Khachik (2003) found a notably higher concentration of antioxidant carotenoids in comparison with two bread wheat varieties of (cvs. Pioneer, Catoctin).

Previous studies have show that significant quantities of fructans are present in wheat grain during grain filling and that vitamin C and glutathione concentrations in immature wheat kernels are much higher than in mature wheat (De Gara et al., 2003). The various physiological effects of fructans and antioxidants may prove beneficial for human health promotion and protection (Nardi et al., 2003). In particular, fructans appear to exert favourable effects on mineral absorption and on pre-biotic activity in experimental animals and in humans (Gibson, 1999, Niness, 1999), on reducing the levels of circulating lipids and glucose (Delzenne and Kok, 1999) and on modulating the immune response (Schley and Field, 2002). The antioxidant activity of whole wheat has been also associated with reduced risk of chronic diseases such as cardiovascular diseases and cancer, even though the preventative mechanisms by which antioxidants prevent the various diseases are still debated (Polidori, 2003). Most studies on fructans have involved inulin, a (2→1)-β-fructan extracted from chicory roots, which are rich in these fructans, as a supplement to normal diets of experimental animals or human volunteers.

Mature wheat, contains low concentration of fructans (1–4%), but is the most important dietary source of fructans, due to the high content of wheat products in the human diet (Van Loo et al., 1995). Thus, wheat with an increased level of fructans would be an interesting natural resource for the preparation of functional foods (Pagani et al., 2003).

The effects of feeding young rats with synthetic balanced diets containing immature and mature durum wheat grain on the immune system, antioxidant status and plasma lipids for two experimental periods were studied. The durum wholemeals were chemically characterized, with particular reference to their carbohydrate and antioxidant contents.