Severino S. Pandiella

Cereal-based fermented foods and beverages

Cereal grains constitute a major source of dietary nutrients all over the world. Although cereals are deficient in some basic components (e.g. essential aminoacids), fermentation may be the most simple and economical way of improving their nutritional value, sensory properties, and functional qualities. This review focuses first on some of the indigenous fermented foods and beverages produced world-wide that have not received the scientific attention they deserve in the last decades. Products produced from different cereal substrates (sometimes mixed with other pulses) fermented by lactic acid bacteria, yeast and/or fungi are included. Finally, newly developed cereal-based foods with enhanced health properties will also be reviewed.

Evaluation of the effect of malt, wheat and barley extracts on the viability of potentially probiotic lactic acid bacteria under acidic conditions

In this work, the effect of cereal extracts, used as delivery vehicles for potentially probiotic lactic acid bacteria (LAB), on the acid tolerance of the cells was evaluated under conditions that simulate the gastric tract. More specifically, the effect of malt, barley and wheat extracts on the viability of Lactobacillus plantarum, Lactobacillus acidophilus and Lactobacillus reuteri during exposure for 4 h in a phosphate buffer acidified at pH 2.5 was investigated. In the absence of cereal extracts all strains demonstrated a significant reduction in their cell population, particularly L. plantarum. The viability of L. plantarum was improved by approximately 4 log(10) cycles in the presence of malt and 3 log(10) cycles in the presence of wheat and barley. The survival of L. acidophilus and L. reuteri was increased by more than 1.5 and 0.7 log(10) cycle, respectively, upon addition of cereal extracts. In order to evaluate the contribution of the cereal constituents on cell survival, the individual effect of glucose, maltose and free amino nitrogen (FAN), which were added at concentrations that correlated to the reducing sugar and FAN content of the cereal extracts, was examined. The viability of L. plantarum was progressively improved as the maltose or glucose concentration increased; an increase by approximately 2 log(10) cycles was observed in the presence of 8.33 g/l sugar. The survival of L. acidophilus increased by more than 1 log(10) cycle, even at very low concentrations of maltose and glucose (e.g., 0.67 g/l), while L. reuteri stability was enhanced in the presence of maltose but no appreciable effect was demonstrated in the presence of glucose. Sugar analysis indicated that glycolysis was inhibited in all cases. Addition of tryptone and yeast extract, used as sources of FAN, enhanced L. acidophilus acid tolerance, but did not affect L. reuteri and L. plantarum. The results presented in this study indicate that malt, wheat and barley extracts exhibit a significant protective effect on the viability of L. plantarum, L. acidophilus and L. reuteri under acidic conditions, which could be mainly attributed to the amount of sugar present in the cereal extracts.

Growth studies of potentially probiotic lactic acid bacteria in cereal-based substrates

Aims: The overall growth kinetics of four potentially probiotic strains (Lactobacillus fermentum, Lact. reuteri, Lact. acidophilus and Lact. plantarum) cultured in malt, barley and wheat media were investigated. The objectives were to identify the main factors influencing the growth and metabolic activity of each strain in association with the cereal substrate.

Microflora identification of the Bulgarian cereal-based fermented beverage boza.

Abstract Many of the indigenous foods consumed around the world are produced by natural fermentation. Information is not always available about the microorganisms involved, which makes it very difficult to maintain the product quality. In this work the microflora of the traditional Bulgarian cereal-based beverage boza was investigated and some of the yeast and lactic acid bacteria strains have been identified and quantified. Although further work is needed to identify what microorganisms are responsible for the beneficial properties of Bulgarian boza these results could form the basis for the improvement of product quality and consistency, and could also be used to develop new cereal-based foods in Western Europe.

Production of potentially probiotic beverages using single and mixed cereal substrates fermented with lactic acid bacteria cultures.

In the present work, single and mixed cereal substrates were fermented with lactic acid bacteria to study and compare the effect of the media formulation on fermentation parameters. Three cereal flours namely malt, barley and barley mixed with malt (barley-malt) were selected and fermented with two probiotic strains: Lactobacillus plantarum (NCIMB 8826) and Lactobacillus acidophilus (NCIMB 8821). The effect of the single and mixed cereal flour suspensions on the fermentation of these two strains of lactic acid bacteria (LAB) was studied at an incubation temperature of 30 °C for 28 h. It was found that the LAB growth was enhanced in media containing malt and significant amounts of lactic acid were produced (0.5-3.5 g/L). A cell concentration between 7.9 and 8.5 Log₁₀ CFU/mL and a pH below 4.0 was achieved within 6 h of fermentation. Though the cell populations in the mixed culture fermentations of mixed substrates were similar to the ones obtained with single cereal flours, significant differences in the production of lactic acid were observed. These results suggest that the functional and organoleptic properties of these cereal-based probiotic drinks could be considerably modified through changes in the substrate or inocula composition.

Discrete particle motion on sieves - A numerical study using the DEM simulation

This paper presents a mathematical investigation of particulate motion on an inclined screening chute using the Discrete Element Method (DEM). Special attention has been paid to the implementation of an apertured boundary and the algorithm for allowing particles to pass through apertures or to rebound when approaching the screen surface. Computational experiments have been conducted to examine the undersize particle motion across the material layer and through the apertures for bimodal mixtures comprising two different sizes of spherical polyethylene pellets. Discrete particle motion at different regions along the screen has been discussed in relation to the physical mechanisms inherent in the solids separation process and their determinative role on screening efficiency. Simulations have demonstrated the negative effect of near-mesh size particles and the positive role of relatively large particles on screening operations and the crucial effect of particle segregation in material layers. Comparison of screening rate along the screen with experiments has demonstrated adequate agreement. This computational study has shown the advantages of using DEM to understand the complex solids separation process. Further works are envisaged to focus on the development of advanced experimental techniques and the implementation of DEM for sieving processes involving moving screens.

Utilisation of whole wheat flour for the production of extracellular pectinases by some fungal strains

The possibility of producing pectinases by Rhizopus stolonifer and Aspergillus awamori, using cereal raw materials as substrate, was investigated. The whole wheat flour acted as a good nutrient source for the cultivation of the microorganisms and exo- and endo-polygalacturonases (PG) were produced in submerged culture. In this respect, it was possible to obtain polygalacturonase activities at an acceptable yield, in comparison with a typical defined medium described in the literature for pectinase production. The synthesis of both enzymes occurred in both strains in the absence of pectin, demonstrating the constitutive nature of these enzymes; nevertheless, production was increased by the addition of a small amount of pectin to the flour.

Influence of malt, wheat, and barley extracts on the bile tolerance of selected strains of lactobacilli

The bile tolerance of three strains of lactobacilli, selected on the basis of their ability to ferment cereal substrates and tolerate simulated gastric transit was examined. Lactobacillus reuteri (NCIMB 1195), L. acidophilus (NCIMB 8821), and L. plantarum (NCIMB 8826) were exposed to 2% bile for 4 h in a phosphate-saline buffer at pH 7. The effects of supplementing the assays with cereal extracts, increasing concentrations of glucose, and free amino nitrogen was also examined. In the absence of any supplements L. reuteri showed the greatest resistance to bile, whilst L. acidophilus displayed the greatest sensitivity. Addition of cereal extracts improved the tolerance of all three strains, barley and wheat extracts imparted similar levels of enhancement in viability, whilst the addition of malt showed a greater positive influence. The extent of improvement was related to the concentration of soluble sugars and FAN present in the cereals, this was illustrated further by the addition of glucose to the assays, as the viability of the organisms was progressively improved with increasing concentrations. The presence of free amino nitrogen also increased bacterial resistance to bile but to a lesser extent both glucose and cereal extracts.

In Vitro Fermentation of Oat Bran Obtained by Debranning with a Mixed Culture of Human Fecal Bacteria

The prebiotic potential of oat samples was investigated by in vitro shaker-flask anaerobic fermentations with human fecal cultures. The oat bran fraction was obtained by debranning and was compared with other carbon sources such as whole oat flour, glucose, and fructo-oligosaccharide. The oat bran fraction showed a decrease in culturable anaerobes and clostridia and an increase in bifidobacteria and lactobacilli populations. A similar pattern was observed in fructo-oligosaccharide. Butyrate production was higher in oat bran compared to glucose and similar to that in fructo-oligosaccharide. Production of propionate was higher in the two oat media than in fructo-oligosaccharide and glucose, which can be used as energy source by the liver. This study suggests that the oat bran fraction obtained by debranning is digested by the gut ecosystem and increases the population of beneficial bacteria in the indigenous gut microbiota. This medium also provides an energy source preferred by colonocytes when it is metabolized by the gut flora.

A numerical simulation of separation of crop seeds by screening: Effect of particle bed depth

Effective separation and grading of cereal grains and crop seeds are of importance in the production of quality cereal foods. This paper presents a two-dimensional numerical study of the separation process of crop seeds by screening, using the Discrete Element Method (DEM) modelling technique. Computational experiments have been conducted for the separation of two common crop seeds, soybeans and mustard seeds, using a vibrating screen. The screening rate and the required screen length at different feeding rates are discussed in relation to the discrete particle motion on the screen. This study has demonstrated the crucial effect of particle bed depth on screening efficiency. For a screening system involving granular materials, the critical feeding rate for the most effective screening operation can be determined via conducting the DEM simulation.