The effects of grape seed extract fortification on the antioxidant activity and quality attributes of bread
Introduction
Phenolic compounds are widely distributed in foods, such as fruits (Robards, Prenzler, Tucker, Swatsitang, & Glover, 1999), vegetables (Bonoli, Gallina Toschi, & Lercker, 2005) and cereals (Dykes and Rooney, 2007, Liyana-Pathirana and Shahidi, 2006). As naturally occurring antioxidants, phenolic compounds have been reported to possess diverse beneficial bioactivities, including anti-allergic, antiviral, anti-inflammatory and anti-mutagenic properties (Yao et al., 2004). Meanwhile, a large number of in vitro and animal studies have also suggested that phenolic compounds may be effective in protecting against cancer, and cardiovascular diseases. The protective effects might be mediated through their action as antioxidants to prevent oxidative damage induced by reactive oxygen species to some important biomolecules (like DNA, lipids and proteins) under pathological conditions (Hollman, 2001, Yao et al., 2004). Recently, phenolic antioxidants have been viewed as an important class of food ingredients either as food additives or as novel ingredients to introduce extra health benefits to various food products. Considering the fact that heat treatment is a widespread processing method in the food industry, a salient question is whether these thermal processes would lead to significant alterations in the antioxidant capacities of phenolic additives. It has been reported that total antioxidant activities of tomatoes and carrots were enhanced with thermal processing (Dewanto et al., 2002, Patras et al., 2009) while antioxidant capacities of soybeans were lowered with similar processing (Xu & Chang, 2008).
So far, little work has been focused on evaluating the relationship between thermal processing of food and changes in antioxidant capacities of phenolic additives. For this consideration, we investigated the influence of thermal processing on antioxidant capacity of grape seed extract (GSE) in the present work. As a well-known nutraceutical product, GSE is an abundant source of catechins and proanthocyanidins with a strong antioxidant and free radical scavenging activity (Liang et al., 2004, Wu et al., 2005). Moreover, it shows other biological effects as well, such as inhibition of platelet aggregation, anti-inflammation and anti-ulcer activity (Saito et al., 1998, Vitseva et al., 2005). In this study, different amounts of GES were mixed with bread ingredients before starting the bread-making program on bread makers. Comparing the antioxidant activities of the GSE-fortified bread with those of standard GSE solutions would enable estimation of the extent to which the thermal process might affect the antioxidant of GSE. Textural analysis, colour measurement and sensory evaluation were also conducted to investigate whether addition of GSE will affect quality attributes of bread or not.
In addition, the effect of GSE on the formation of Nε-(carboxymethyl)lysine (CML) in bread was studied. As a well-characterised detrimental advanced glycation endproduct (AGE) (Sebekova and Somoza, 2007, Tessier and Niquet, 2007), CML was widely found in a range of foods including bread (Charissou et al., 2007, Hartkopf and Erbersdobler, 1994) and its content in crust was reported to be much higher than in crumb (Assar, Moloney, Lima, Magee, & Ames, 2009). Currently it is viewed as a potential toxicant in food. Moreover, it has become a biomarker associated with oxidative stress, atherosclerosis and diabetes in humans (Nerlich and Schleicher, 1999, Schleicher et al., 1997). Natural antioxidants like bean extracts (Madhujith, Amarowicz, & Shahidi, 2004), peanut skin and some flavonoids have been proven to possess strong inhibitory effects on the formation of AGEs in vitro, which are mainly attributed to their potent antioxidant activities (Lou et al., 2001, Peng et al., 2007, Wu and Yen, 2005). In addition, capability of certain phenolics such as tea catechins and proanthocyanidins to scavenge reactive carbonyl species (such as glyoxal, methylglyoxal) in glycation process has also been proposed to contribute to inhibition of AGE formation (Lo et al., 2006, Peng et al., 2008). Therefore, it is of great interest to investigate whether GSE fortification could reduce CML content in bread. In this regard, influence of different levels of GSE addition on CML content of bread was examined.
Section snippets
Chemicals
Ingredients for bread-making were bought from a local supermarket in Hong Kong. Grape seed extract with 95% proanthocyandins including catechin and epicatechin was a gift from Shenzhen BannerBio Inc. (Shenzhen, PR China). The compound Nε-(carboxymethyl)lysine (CML) was purchased from NeoMPS (Strasbourg, France). Ortho-phthalaldehyde (OPA), 2-mercaptoethanol, sodium borohydride, boric acid, sodium tetraborate decahydrate, sodium hydroxide, hydrochloric acid,
Results and discussion
Thermal treatment is among the most popular ways of food processing. During heating, a complex array of chemical reactions takes place, which plays a pivotal role in determining the quality attributes (sensory characteristics, nutritional value and safety) of processed foods. While some compounds are destroyed during food processing, many more new compounds might be introduced into the food system. Some of these compounds contribute significantly to the organoleptic properties of foods, such as
Conclusions
Thermal processing decreased the antioxidant activity of GSE additive in bread. However, using GSE as an additive could greatly enhance the total antioxidant capacity of bread, and at the same time, decrease the level of CML. Our results also demonstrated that with appropriate levels of addition, GSE could lead to a favourable change in the colour of bread without causing significant changes in other sensory properties. Altogether, GSE-fortified bread is promising to be developed as a
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