Use of sourdough fermentation and pseudo-cereals and leguminous flours for the making of a functional bread enriched of γ-aminobutyric acid (GABA)

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Abstract

Lactobacillus plantarum C48 and Lactococcus lactis subsp. lactis PU1, previously selected for the biosynthesis of γ-aminobutyric acid (GABA), were used for sourdough fermentation of cereal, pseudo-cereal and leguminous flours. Chickpea, amaranth, quinoa and buckwheat were the flours most suitable to be enriched of GABA. The parameters of sourdough fermentation were optimized. Addition of 0.1 mM pyridoxal phosphate, dough yield of 160, inoculum of 5 × 107 CFU/g of starter bacteria and fermentation for 24 h at 30 °C were found to be the optimal conditions. A blend of buckwheat, amaranth, chickpea and quinoa flours (ratio 1:1:5.3:1) was selected and fermented with baker's yeast (non-conventional flour bread, NCB) or with Lb. plantarum C48 sourdough (non-conventional flour sourdough bread, NCSB) and compared to baker's yeast started wheat flour bread (WFB). NCSB had the highest concentration of free amino acids and GABA (ca. 4467 and 504 mg/kg, respectively). The concentration of phenolic compounds and antioxidant activity of NCSB bread was the highest, as well as the rate of in vitro starch hydrolysis was the lowest. Texture analysis showed that sourdough fermentation enhances several characteristics of NCSB with respect to NCB, thus approaching the features of WFB. Sensory analysis showed that sourdough fermentation allowed to get good palatability and overall taste appreciation.

Introduction

γ-Aminobutyric acid (GABA), a four-carbon non-protein amino acid, acts as the major inhibitory neurotransmitter of the central nervous system (Krnjevic, 1974). Other physiological functions of GABA are induction of anti-hypertensive, prevention of diabetes, diuretic and tranquilizer effects (Jakobs et al., 1993, Cohen et al., 2002, Komatsuzaki et al., 2005, Adeghate and Ponery, 2002, Hagiwara et al., 2004). As the consequence, GABA is extensively used in pharmaceutical preparations and functional foods such as gammalone, dairy products, gabaron tea and shochu (Nomura et al., 1999, Sawai et al., 2001, Yokoyama et al., 2002). Glutamate decarboxylase (GAD) is the enzyme which catalyses the conversion of l-glutamate (or its salts) onto GABA, through a single-step α-decarboxylation (Ueno, 2000, Battaglioli et al., 2003).

The capacity of lactic acid bacteria to synthesize GABA was also investigated with the aim of producing functional fermented foods (Komatsuzaki et al., 2005, Komatsuzaki et al., 2008, Siragusa et al., 2007, Rizzello et al., 2008a, Rizzello et al., 2008b). Pickled vegetables, and fermented meats and fishes were enriched of GABA using selected lactic acid bacteria starters (Komatsuzaki et al., 2005). Several GABA-enriched cereal foods are also manufactured: rice germ soaked in water, germinated brown rice treated by high-pressure, and germinated wheat and red-mold rice containing Monascus fungus (Siragusa et al., 2007). Only one study considered the production of a sourdough wheat bread enriched of GABA (Rizzello et al., 2008a, Rizzello et al., 2008b). Overall, sourdough lactic acid bacteria have a well known role in improving the sensory, texture, nutritional and shelf-life properties of cereal-based baked goods. As previously stated, sourdough fermentation improves nutritional aspects, texture and palatability of whole grain, fibre rich or gluten-free products (De Angelis et al., 2007); stabilizes or increases the level of various bioactive compounds; delays the starch bioavailability thus decreasing the glycemic index; and increases the mineral bioavailability (De Angelis et al., 2007). Beyond the potential of sourdough fermentation, the selection of cereal, pseudo-cereal and/or leguminous substrates based on their nutritional and healthy potential is also of key importance to get optimal technology, sensory and healthy properties. For instance, the supplementation of wheat flour with high-protein-content legume flours (e.g., bean and chickpea flours) improves the nutritional quality of baked goods and satisfies the consumption of vegetarian people since legume flours are rich in lysine and have the potential to overcome protein-calorie malnutrition (Gómez et al., 2008). Based on the total grain production, chickpea (Cicer arietinum L.), an annual herbage plant, is the third most important grain legume in the world (FAO, 1994). Proteins of chickpea are considered a suitable source of dietary proteins due to their optimal balance between essential amino acids, high bioavailability and low level of anti-nutritional factors (Clemente et al., 1999). Pseudo-cereals such as buckwheat, amaranth and quinoa may have texture and nutritional features which make them suitable for replacing, at least in part, traditional cereal-based products. In particular, buckwheat has a high concentration of dietary fibres and micro-nutrients (Schoenlechner et al., 2008), amaranth is a source of technologically useful proteins which also have an antifungal effect (Rizzello et al., 2009), and quinoa contains high nutritional quality fatty acids (Schoenlechner et al., 2008). The optimal combination of selected lactic acid bacteria and flours with high nutritional potential may lead to the manufacture of sourdough fermented baked goods highly enriched of GABA.

This study aimed at selecting non-conventional flours for the making of sourdough bread enriched of GABA, which also showed agreeable nutritional, texture and sensory characteristics.

Section snippets

Microorganisms and culture conditions

Lactobacillus plantarum C48 and Lactococcus lactis subsp. lactis PU1 were previously isolated from cheeses and selected for the capacity of synthesizing GABA (Siragusa et al., 2007). Lb. plantarum C48 was cultivated for 24 h at 30 °C in MRS broth (Oxoid, Basingstoke, Hampshire, England), with the addition of fresh yeast extract (5%, v/v) and 28 mM maltose at the final pH of 5.6. Lc. lactis subsp. lactis PU1 was cultivated for 24 h at 30 °C in M17 broth (Oxoid). When used for sourdough fermentation,

Selection of flours

The twelve flours used in this study had various endogenous concentrations of GABA (Table 4). Controls CT0 (not incubated) contained GABA at levels which varied from 3 ± 1 to 78 ± 13 mg/kg. The highest values were found for buckwheat and quinoa flours (40 ± 6 and 78 ± 13 mg/kg, respectively). The concentration of Glu varied from 30 ± 5 to 1133 ± 23 mg/kg. When doughs were incubated for 24 h at 30 °C, in the presence of erythromycin and without bacterial inoculum (CTi), the concentration of GABA increased and

Discussion

Pseudo-cereal and leguminous flours have some nutritional and functional features preferable to cereal flours (Fessas et al., 2008, Escudero et al., 2004, Aluko and Monu, 2003). Proteins, especially those of pseudo-cereals, are highly soluble and characterized by foaming and emulsifying properties (Schoenlechner et al., 2008). The amino acid profile of the proteins of amaranth is comparable to that of egg, and the nutritional quality of the proteins of quinoa is comparable to that of caseins (

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