| Abstract |
Maximizing the utilization of cereal by-products has received great attention all over the world, because of their great nutritional and therapeutic properties. In China, the Ministry of Agriculture and Rural Affairs created the National Rural Industry Development Plan (2020-2025) in 2020 to encourage the full utilization of cereal by-products, such as rice husks, rice bran and wheat bran. New and unconventional sources of probiotics may provide unique health efficacy by producing healthy bioactive compounds, which can be used to improve the nutritional values of cereal by-products. The current study evaluates the effect of Lactobacillus apis as a novel strain isolated from the bumblebee gut, two different Lactobacillus communities isolated from human breast milk (LC-BM) and camel milk (LC-CM) on the nutritional properties and bioactivity of rice bran and wheat bran. Lactobacillus plantarum and Saccharomyces cerevisiae, as the most common strains used in cereals fermentation, were used to compare their fermentation efficiency with the new isolated strains. These new strains may provide promising strategies to improve rice bran's and wheat bran's nutritional value and therapeutic properties by reducing the anti-nutritional factors and improving the bioactive compounds. The main results of this study are summarized as follows:
In the first part, the impact of different strains isolated from different sources on rice bran's bioactivity, nutritional, and therapeutic properties was measured. The in vitro antioxidant activity of rice bran increased significantly in the fermented samples at different fermentation times compared to unfermented samples. The highest enhancement of the antioxidant activity based on DPPH • and ABTS •+ scavenging ability was seen in the samples fermented with LC-CM and L. apis, the IC 50 DPPH • and IC 50 ABTS •+ ranging from 11.32 to 11.15 µL/mL and 11.34 to 10.75 µL/mL, respectively. Furthermore, the samples fermented with LC-BM showed the lowest IC 50 metal chelating capacity (11.79 µL/mL). While L. plantarum fermented samples showed the highest hydroxyl radical scavenging activity compared to the other fermented samples. In addition, L. apis fermented samples had the highest FRAP value (149.63 mMFe 2+ /mL) compared to the other samples. This improvement in antioxidant activity has been positively associated with certain metabolic compounds released during fermentation, such as dihydrosinapic acid, hydroferulic acid, inositol, vinyl phenol, ketostearic acid, p-coumaric acid, and pyruvic acid. All strains improved the volatile profile of rice bran, and the fermented rice bran by each strain displayed a unique volatile composition. Fermented rice bran samples displayed a significant increase of niacin, pyridoxine, riboflavin and thiamin compared to unfermented samples, with significant differences observed among different fermented samples. In addition, the in vitro cytotoxicity test showed that the fermented broths had a significant increase in anticancer activity against the HT-29 cell line, and the samples fermented with LC-BM and LC-CM showed higher anticancer activity.
In the second part, wheat bran is the most abundant cereal by-product, which has not been
optimally exploited. This study reveals the application of new probiotic strains isolated from untraditional sources in wheat bran to maximize its utilization. Compared to the most popular strains (S. cerevisiae and L. plantarum), LC-BM and LC-CM showed a greater ability to enhance the antioxidant activity of wheat bran through DPPH • , ABTS •+ and hydroxyl radical scavenging ability, metal chelating ability, and ferric-reducing antioxidant power (FRAP). Furthermore, LC-BM and LC-CM increased the antioxidant activity of wheat bran based on most tests more significantly than L. apis, which showed similar effects with L. plantarum. This improvement in wheat bran antioxidant activity has been associated with changes of some metabolic compounds, such as p-coumaric acid, o-coumaric acid, 2-hydroxycinnamic acid, gentiobiose, pyruvic acid, dihydrosinapic acid and vinyl phenol. Additionally, all strains significantly improved the volatile profile of wheat bran, and the samples fermented by each strain displayed a unique volatile composition. LC-CM and LC-BM significantly increased the levels of most free amino acids, conditional amino acids and branched-chain amino acids of wheat bran. The highest content of γ-aminobutyric acid was seen in the samples fermented with S. cerevisiae for 72 and 12 h (247.42 mg/L and 199.98 mg/L), followed by the samples fermented with L. apis for 72 h (156.02 mg/L). Meanwhile, LC-BM and LC-CM remarkably increased the content of organic acids and water-soluble vitamins in wheat bran. Moreover, we found that LC-CM significantly increased the cytotoxicity activity of wheat bran against HT-29 cells, followed by L. apis.
In the third part, the rice bran samples fermented with different strains for 48 h (showing the best bioactivity) obtained in the first part were chosen to study their bioactivities and bioaccessibility during in vitro digestion. The anti-nutritional factors decreased significantly in the RBF-LCCM and RBF-LCBM samples, which reached 1.2 g/100g of phytic acid and 0.77 mg/g of oxalate, respectively. The RBF-LA, RBF-LCBM and RBF-LCCM samples had the highest protein quality compared to other fermented and unfermented samples during in vitro digestion. After in vitro digestion, the fermented samples showed a significant increase in the bioaccessibility of minerals, the calcium in the RBF-LP samples reaching 65.69 ± 0.75% and the iron in the RBF-LP samples reaching 76.66 ± 0.69%. Free phenolic content in fermented samples increased significantly after in vitro digestion, which ranged between 9.09 ± 0.65 mg GAE g -1 to 12.33 ± 0.47 mg GAE g -1. While the free phenolic content in the unfermented samples was 5.71 ± 0.21 mg GAE g -1. In the same context, the RBF-LA and RBF-LCBM samples showed the highest increase of TPC, antioxidant activity and capacity of phenolic extracts during in vitro digestion. The highest bioaccessible phenolic compounds were p-coumaric acid (38.49 ± 0.54 µg/g) in the RBF-LCBM samples, followed by gallic acid (25.90 ± 0.37 µg/g) in the RBF-SC samples. While the highest bioaccessible phenolic compound in the unfermented samples was epicatechin (14.38 ± 0.08 µg/g). Additionally, phenolic compounds in the fermented samples released during in vitro digestion inhibited the α-amylase and α-glucosidase activity significantly compared to unfermented samples.
In the fourth part, fermented rice bran broths (FRBBs) obtained in the first part with the best bioactivity (fermented for 48 h) had been mixed with 1% chitosan in four concentrations (5, 10, 15 and 20%) to make films for possible use as active food packaging. Firstly, the physicochemical properties, microstructure, and bioactivities of the films were evaluated to determine the best ratio of FRBBs. The results showed that the films with 10% FRBB addition displayed the optimal physico-mechanical properties. The tensile strength (TS) and elongation at break (EB) increased significantly from 3.21 ± 0.93 Mpa and 49.0 ± 14.16% in the control chitosan film (CH) to 9.85 ± 0.46 Mpa and 91.31 ± 1.65% in the FRB-LCBM film, and 9.61 ± 0.81 and 88.64 ± 4.74% in the FRB-LA film. The microstructure of the films with FRBBs exhibited homogeneous, plane, smooth, and compact surfaces with some white spots. The combination of FRBBs with CH produced more highly bioactive films than chitosan alone. These prepared films were used to improve the shelf life of salmon fillets. The effect of the film packaging on the shelf life of salmon fillets was evaluated according to the salmon moisture content, pH, thiobarbituric acid (TBA), total volatile basic nitrogen (TVB-N), K value, color, free amino acids (FAA), and microbial count during storage at 4 °C for 12 days. The chitosan films prepared with different FRBBs had a positive effect on the shelf life of salmon fillets, leading to the lowest changes in pH (from 6.32 to 6.55), moisture content (from 55.8 to 60.3%), TBA value (from 2.30 to 3.75 mg MDA/Kg), TVB-N content (from 14.25 to 19.85 mg TVB-N/100g), and k value (ranged from 32.86 to 47.70%). Salmon fillets covered by chitosan combined with FRBBs films retained their bright red color to a greater degree than the uncovered samples and the samples covered with the control chitosan films. Most of the treated salmon fillets with chitosan combined with FRBBs films showed the lowest rate of protein degradation during storage, having the lowest content of free amino acids. Moreover, the addition of the different FRBBs significantly improved the ability of the chitosan films to reduce microbial growth in salmon fillets during storage. In conclusion, chitosan films prepared with 10% of FRBBs could form high-quality films that can effectively prolong the shelf life of salmon fillets.
In summary, this study revealed the excellent probiotic properties of lactic acid bacteria isolated from non-traditional sources and demonstrated their applications in improving the nutritional and functional properties of rice bran and wheat bran, which provides a possible way to improve the utilization of rice bran and wheat bran.
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