Owing to their health benefits, probiotics and prebiotics are nowadays widely used in yogurts and fermented milks, which are leader products of functional foods worldwide. The world market for functional foods has grown rapidly in the last three decades, with an estimated size in 2003 of ca US$ 33 billion, while the European market estimation exceeded US$ 2 billion in the same year. However, the production of probiotics and prebiotics at industrial scale faces several challenges, including the search for economical and abundant raw materials for prebiotic production, the low-cost production of probiotics and the improvement of probiotic viability after storage or during the manufacturing process of the functional food. In this review, functional foods based on probiotics and prebiotics are introduced as a key biotechnological field with tremendous potential for innovation. A concise state of the art addressing the fundamentals and challenges for the development of new probiotic- and prebiotic-based foods is presented, the niches for future research being clearly identified and discussed.

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Agroindustrial by-products derived from fruit processing are an important source of biocompounds that can be used as functional food ingredients. The objective of this work was to evaluate cactus pear and pineapple peel flours as an alternative carbon source during fermentation using bacteria with probiotic potential. The total fibre content of both flours was over 60%, with total soluble carbohydrate content around 20%, indicating a good carbon source for lactic acid bacteria. Kinetic parameters indicate that peel flours are a suitable carbon source because the lactic acid bacteria grow (mean growth rate constant, k, values close to glucose, 1.52 h) and acidify the culture media (maximum acidification rate, V max , approximately 1.60 pH 9 10 À3 min À1 ). There was no difference in prebiotic potential or prebiotic activity score for both the peel flours. Pediococcus pentosaceus performs better during fermentation. In this respect, cactus pear and pineapple peel flours can be used as functional ingredients due to their fermentable properties.Fruit peels as functional ingredients J. Diaz-Vela et al. Fruit peels as functional ingredients J. Diaz-Vela et al. Strain Carbon source pH final N (Log CFU mL À1 ) Pediococcus pentosaceus UAM22 Glucose (control) 4.39 AE 0.28 C,a 9.52 AE 0.25 A,a Cactus pear flour 5.81 AE 0.35 C,a 9.65 AE 0.25 A,a Pineapple flour 4.89 AE 0.42 C,a 9.56 AE 0.31 A,a Aerococcus viridans UAM21 Glucose (control) 6.12 AE 0.63 B,a 9.22 AE 0.24 B,a Cactus pear flour 5.64 AE 0.85 B,a 8.73 AE 0.25 B,a Pineapple flour 7.88 AE 0.21 B,a 9.33 AE 0.13 B,a Lactobacillus rhamnosus GG Glucose (control) 5.82 AE 0.57 C,a 9.24 AE 0.27 B,a Cactus pear flour 4.63 AE 0.85 C,a 8.77 AE 0.15 B,a Pineapple flour 5.15 AE 0.56 C,a 9.38 AE 0.26 B,a Escherichia coli K12 Glucose (control) 5.91 AE 0.21 A,a 8.46 AE 0.11 C,a Cactus pear flour 6.29 AE 0.14 A,a 8.63 AE 0.24 C,a Pineapple flour 6.68 AE 0.42 A,a 8.21 AE 0.22 C,a A, B, C, D means with same letter in same column are not significantly different (P > 0.05) for strain type. a, b means with same letter in same column are not significantly different (P > 0.05) for carbon source. Pediococcus pentosaceus UAM22 Cactus pear flour 0.33 AE 0.03 A,a Pineapple flour 0.32 AE 0.01 A,a Aerococcus viridans UAM21 Cactus pear flour À0.03 AE 0.02 C,a Pineapple flour 0.09 AE 0.02 C,a Lactobacillus rhamnosus GG Cactus pear flour 0.19 AE 0.01 B,a Pineapple flour 0.21 AE 0.02 B,aA, B, C means with same letter in same column are not significantly different (P > 0.05) for strain type. a, b means with same letter in same column are not significantly different (P > 0.05) for carbon source.Fruit peels as functional ingredients J. Diaz-Vela et al.

This study deals with the ability of probiotic bacteria to ferment prebiotics in vitro to estimate the prebiotic activity score and prebiotic index based on specific substrates and strains. Five probiotic bacteria were isolated from commercial products and their fermentation capability of three commercial prebiotics was assessed. Growth kinetics of probiotics showed that all of them were able to use the prebiotics as carbon sources. Mostly bacteria grew faster on Frutafit and Dligomate 55 than on lactulose. The prebiotic activity score and prebiotic index concepts were introduced to evaluate the performance of every probiotic with each prebiotic; accordingly, the highest values were for L. rhamnosus on Dligomate 55, while the worst according to these parameters was L. casei Shirota on Frutafit. Prebiotic index and prebiotic activity score describe well the selective growth of probiotics supported by prebiotics; therefore, they could be useful tools to define adequate combinations in colonic foods development.

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