Effect of citral nanoemulsion on the inactivation of Listeria monocytogenes and sensory properties of fresh-cut melon and papaya during storage.

This study evaluated the survival of Listeria monocytogenes on fresh-cut melon and papaya treated with citral nanoemulsion (CN) during 7 days of storage at 4, 8, 12, and 16 °C. CN was prepared by catastrophic phase inversion, and fresh-cut melon and papaya were artificially inoculated, resulting in 5 log cfu/g of L. monocytogenes. Then, they were treated with 0.30 (CN-0.3) and 0.15 (CN-0.15) µL/mL of CN. CN presented droplet size below 200 nm, monodisperse distribution, and negative surface charge. CN-0.3 reduced the L. monocytogenes counts more efficiently, with counts below the detection limit (1 log cfu/g) in both fruits after 48 h at 4 °C, and 72 h at 8 °C and 12 °C. At 16 °C, L. monocytogenes counts were below the detection limit for CN-0.3 after 120 h in papaya, but it survived the other treatments for 7 days. Both CN-0.3 and CN-0.15 decreased the indigenous microbiota. Scanning electron microscopy (SEM) showed bubbles in L. monocytogenes membrane and cell disruption in fruits treated with CN-0.3. Finally, CN-0.3 treated melon and papaya showed greater brightness, herbal flavor and aroma, firmness, and juiciness, as well as lower sugar and organic acid profile changes than the control samples during storage. Results indicate citral nanoemulsion's efficiency in controlling L. monocytogenes growth on fresh-cut melon and papaya stored at refrigerated temperatures without negatively influencing the sensory parameters.

Growth behavior of low populations of Listeria monocytogenes on fresh-cut mango, melon and papaya under different storage temperatures.

The growth behavior of Listeria monocytogenes low population (1-4 cells/sample) on fresh-cut mango, melon, papaya and fruit mix stored at 4, 8, 12 and 16 °C was evaluated over 10 days. Mango showed the lowest counts for L. monocytogenes during 10 days regardless of storage temperature (<1.7 log cfu.g-1). Melon supported high bacterial growth over 10 days, reaching 5 log cfu.g-1 at 16 °C. Both the fruit and storage temperature influenced the Listeria low population growth potential (δ). Cumulative frequency distribution of L. monocytogenes showed that after 10 days, 100% of fresh-cut fruits and fruit mix stored at 4 °C remained ≤2 log cfu.g-1, while at 12 and 16 °C 100% of melon, papaya and fruit mix samples exceeded this limit. At 8 °C, 100% of mango and fruit mix samples remained below this limit after 10 days, whereas 100% of melon and papaya reached it after 7 days. Results indicate 4 °C as the ideal to store safely fresh-cut mango, melon, papaya and fruit mix for 10 days. Besides, 8 °C can also be an option, but not for melon and papaya. Findings highlight the ability of L. monocytogenes to survive and grow in fresh-cut fruits even at a very low initial population levels.

Effects of Lactobacillus acidophilus LA-3 on physicochemical and sensory parameters of açaí and mango based smoothies and its survival following simulated gastrointestinal conditions.

The effects of the incorporation of Lactobacillus acidophilus LA3 (inoculated at 9 log CFU/mL) on physicochemical parameters, contents of sugars and organic acids, phenolic profile and sensory aspects of açaí (AS) and mango based smoothies (MS) during 28 days of refrigerate storage were assessed. The survival of L. acidophilus in AS and MS under simulated human gastrointestinal conditions during storage was also monitored. Counts of L. acidophilus LA-3 were approximately 8.5 log CFU/mL in AS and 7.5 log CFU/mL in MS after 1 day of storage and no changes (p ≥ 0.05) were observed in later evaluated storage time periods. Fruit smoothies (AS or MS) with L. acidophilus LA-3 presented lower (p < 0.05) contents of glucose, fructose and maltose and higher (p < 0.05) contents of lactic and succinic acids compared to those without L. acidophilus LA-3. Phenolic contents increased or decreased (p < 0.05) after 1 day of storage in AS and MS with L. acidophilus LA-3 and did not change (p ≥ 0.05) in AS or MS without L. acidophilus LA-3. The incorporation of L. acidophilus LA-3 increased the acidic flavor and fermented aroma in AS and MS. Viable counts of L. acidophilus LA-3 were approximately 7.5 and 8.5 log CFU/mL in AS and MS, respectively, at the end of in vitro digestion just after the incorporation, as well as on days 14 and 28 of storage. These results show the feasibility of incorporating L. acidophilus LA-3 into AS or MS and suggest these fruit smoothies as matrices for formulation of non-dairy beverages containing potentially probiotic lactobacilli.

The performance of five fruit-derived and freeze-dried potentially probiotic Lactobacillus strains in apple, orange, and grape juices.

BACKGROUND: This study assessed the survival of the fruit-derived and freeze-dried L. plantarum 49, L. brevis 59, L. paracasei 108, L. fermentum 111 and L. pentosus 129 strains during frozen storage and when incorporated into apple, orange, and grape juice stored under refrigeration. Physicochemical parameters of juices containing the freeze-dried Lactobacillus strains and the survival of the test strains in the fruit juices during in vitro digestion were also evaluated. RESULTS: No decreases in survival rates (log N/log N0) of the freeze-dried cells were observed in up to 1 month of storage. The survival rates of the freeze-dried strains L. plantarum 49 and L. paracasei 108 were > 0.75 in up to 4 months of storage. All freeze-dried strains exhibited survival rates of >0.75 in up to 2 weeks of storage in apple juice; only L. plantarum 49 and L. paracasei 108 showed similar survival rates in orange and grape juices in up to 2 weeks of storage. The contents of the monitored organic acids or sugars during storage varied depending on the added strain and the type of fruit juice. At the end of in vitro digestion, L. brevis 59, L. paracasei 108 and L. fermentum 111 showed survival rates of >0.80 in apple juice. CONCLUSION: Apple juice was the best substrate for the survival of the tested freeze-dried Lactobacillus strains over time. L. paracasei 108 and L. plantarum 49 were the strains presenting the best performance for incorporation in potentially probiotic fruit juices. © 2018 Society of Chemical Industry.