Abstract
This study aimed to identify lactic acid bacteria (LAB) in byproducts of fruit (Malpighia glabra L., Mangifera indica L., Annona muricata L., and Fragaria vesca L.) pulp processing. Fifty strains of LAB were identified using matrix-assisted laser desorption/ionization–time of flight mass spectrometry (MALDI-TOF MS) and 16S rRNA gene sequence (16S rRNA) analysis. Species belonging to Lactobacillus genus were the predominant LAB in all fruit pulp processing byproducts. The average congruency between the MALDI-TOF MS and 16S rRNA in LAB species identification reached 86%. Isolates of L. plantarum, L. brevis, L. pentosus, L. lactis and L. mesenteroides were identified with 100% congruency. MALDI-TOF MS and 16S rRNA analysis presented 86 and 100% efficiency of LAB species identification, respectively. Further, five selected Lactobacillus strains (L. brevis 59, L. pentosus 129, L. paracasei 108, L. plantarum 49, and L. fermentum 111) were evaluated for desirable probiotic-related properties and growth behavior on two different cultivation media. The exposure to pH 2.0 sharply decreased the counts of the different Lactobacillus strains after a 1 or 2 h incubation, while varied decreases were noted after 3 h of exposure to pH 3.0. Overall, the exposure to pH 5.0 and to bile salts (0.15, 0.30, and 1.00%) did not decrease the counts of the Lactobacillus strains. All tested Lactobacillus strains presented inhibitory activity against Staphylococcus aureus, Salmonella Typhimurium, Salmonella Enteritidis, Listeria monocytogenes and Escherichia coli, and presented variable susceptibility to different antibiotics. The selected Lactobacillus strains presented satisfactory and reproducible growth behavior. In conclusion, MALDI-TOF MS and 16S rRNA analysis revealed high efficiency and congruency for LAB species identification, and the selected Lactobacillus strains may be candidates for further investigation of novel probiotic strains.
Highlights
Consumption of fruit and fruit products has been increasing due to growing recognition of their nutritional value associated with their high content of minerals, vitamins, and secondary phytochemical compounds (Rufino et al, 2010; Silva et al, 2014)
This study aimed (i) to isolate and identify lactic acid bacteria (LAB) in fruit pulp processing byproducts using MALDI-TOF MS and 16S rRNA gene sequence analysis, as well as to verify the identification congruency between the two techniques; (ii) to assess the probiotic properties of selected Lactobacillus strains in vitro, including acid tolerance, bile tolerance, and capability to inhibit pathogenic food-related bacteria; and (iii) to verify the antibiotic resistance and growth behavior of the selected Lactobacillus strains in different cultivation media
MALDI-TOF MS has been introduced for the identification of microorganisms, and it has been suggested as a key tool in food safety and control (Jadhav et al, 2015; Nomura, 2015)
Summary
Consumption of fruit and fruit products (mostly low-processed juices and frozen pulps) has been increasing due to growing recognition of their nutritional value associated with their high content of minerals, vitamins, and secondary phytochemical compounds (Rufino et al, 2010; Silva et al, 2014). The processing of fruit generates a great amount of industrial byproducts, representing 10–60% of the total fruit weight (Ayala-Zavala et al, 2010). These byproducts comprise peels, rinds, seeds, and unused flesh, which are usually inappropriately discarded in the environment, leading to waste accumulation, and negative environmental impacts (Ajila et al, 2007; Araújo et al, 2014). In addition to the known potential use of tropical fruit pulps and their byproducts for the isolation of phytochemicals for application in nutraceutical supplements (Ayala-Zavala et al, 2011), these byproducts exhibit a wide variety of microorganisms of interest to the food industry (Yang et al, 2010), especially lactic acid bacteria (LAB). The microbial populations of raw fruit commonly vary between 5 and 7 log CFU/g, where LAB constitute a small part (2– 4 log CFU/g) of the autochthonous microbiota (Di Cagno et al, 2010a,b, 2011a,b)
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