Bacterial cellulose (BC) is widely used in the food industry for products such as nata de coco. The mechanical properties of BC hydrogels, including stiffness and viscoelasticity, are determined by the hydrated fibril network. Generally, Komagataeibacter bacteria produce gluconic acids in a glucose medium, which may affect the pH, structure and mechanical properties of BC. In this work, the effect of pH buffer on the yields of Komagataeibacter hansenii strain ATCC 53582 was studied. The bacterium in a phosphate and phthalate buffer with low ionic strength produced a good BC yield (5.16 and 4.63 g/l respectively), but there was a substantial reduction in pH due to the accumulation of gluconic acid. However, the addition of gluconic acid enhanced the polymer density and mechanical properties of BC hydrogels. The effect was similar to that of the bacteria using glycerol in another carbon metabolism circuit, which provided good pH stability and a higher conversion rate of carbon. This study may broaden the understanding of how carbon sources affect BC biosynthesis.
Essential oils (EOs) have good natural antioxidant and antimicrobial properties; however, their volatility, intense aroma, poor aqueous solubility, and chemical instability limit their applications in the food industry. The encapsulation of EOs in β-cyclodextrins (β-CDs) is a widely accepted strategy for enhancing EO applications. The complexation of cinnamon essential oil (CEO) with five types of β-CDs, containing different substituent groups (β-CD with primary hydroxyl, Mal-β-CD with maltosyl, CM-β-CD with carboxymethyl, HP-β-CD with hydroxypropyl, and DM-β-CD with methyl), inclusion process behaviors, volatile components, and antioxidant and antibacterial activities of the solid complexes were studied. The CEOs complexed with Mal-β-CD, CM-β-CD, and β-CD were less soluble than those complexed with DM-β-CD and HP-β-CD. Molecular docking confirmed the insertion of the cinnamaldehyde benzene ring into various β-CD cavities via hydrophobic interactions and hydrogen bonds. GC-MS analysis revealed that HP-β-CD had the greatest adaptability to cinnamaldehyde. The CEO encapsulated in β-, Mal-β-, and CM-β-CD showed lower solubility but better control-release characteristics than those encapsulated in DM- and HP-β-CD, thereby increasing their antioxidant and antibacterial activities. This study demonstrated that β-, Mal-β-, and CM-β-CD were suitable alternatives for the encapsulation of CEO to preserve its antioxidant and antibacterial activities for long-time use.
Summary
Plant essential oils have great potential to become a new generation of marine fish preservatives, and the key to the application of essential oil in fresh‐keeping is to improve its cost performance. In this study, the combined effect of 0.008 g/mL lemongrass essential oils and 0.01 g/mL cinnamon essential oils with different concentration (0, 0.005, 0.01, 0.03, 0.05 g/mL) of tea polyphenols on the antioxidant activity and antimicrobial activity in vitro, and application in marine fish preservation was studied. The in vitro tests showed that the combination of essential oils with tea polyphenols increased the antioxidant and antimicrobial activities compared with the essential oils or tea polyphenols alone. During the preservation of the marine fish Dusky Spinefoot, the combination of essential oils with tea polyphenols slightly inhibited microbial growth, but greatly reduced the visible decay on the surface of fish flavour deterioration and biogenic amine production. Antimicrobial activities were also observed in films prepared combining essential oil and tea polyphenols. These combined effects are meaningful and provide prospects for expanding the application of essential oil and developing a new hurdle technology for marine fish storage.
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