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Co-culture is known as an efficient way to explore the metabolic potential of fungal strains for new antibiotics and other therapeutic agents that could counter emerging health issues. To study the effect of co-culture on the secondary metabolites and bioactivities of two marine strains, Aspergillus terreus C23-3 and Aspergillus. unguis DLEP2008001, they were co-cultured in live or inactivated forms successively or simultaneously. The mycelial morphology and high-performance thin layer chromatography (HPTLC) including bioautography of the fermentation extracts were recorded. Furthermore, the agar cup-plate method was used to compare the antimicrobial activity of the extracts. Based on the above, liquid chromatography-photodiode array-tandem mass spectrometry (LC-PDA-MS/MS) together with Global Natural Products Social molecular networking (GNPS) and multiple natural products database mining were used to further analyze their secondary metabolite variations. The comprehensive results showed the following trends: (1) The strain first inoculated will strongly inhibit the growth and metabolism of the latter inoculated one; (2) Autoclaved A. unguis exerted a strong inducing effect on later inoculated A. terreus, while the autoclaved A. terreus showed high stability of its metabolites and still potently suppressed the growth and metabolism of A. unguis; (3) When the two strains are inoculated simultaneously, they both grow and produce metabolites; however, the A. terreus seemed to be more strongly induced by live A. unguis and this inducing effect surpassed that of the autoclaved A. unguis. Under some of the conditions, the extracts showed higher antimicrobial activity than the axenic cultures. Totally, A. unguis was negative in response but potent in stimulating its rival while A. terreus had the opposite effect. Fifteen MS detectable and/or UV active peaks showed different yields in co-cultures vs. the corresponding axenic culture. GNPS analysis assisted by multiple natural products databases mining (PubChem, Dictionary of Natural Products, NPASS, etc.) gave reasonable annotations for some of these peaks, including antimicrobial compounds such as unguisin A, lovastatin, and nidulin. However, some of the peaks were correlated with antagonistic properties and remain as possible novel compounds without mass or UV matching hits from any database. It is intriguing that the two strains both synthesize chemical 'weapons' for antagonism, and that these are upregulated when needed in competitive co-culture environment. At the same time, compounds not useful in this antagonistic setting are downregulated in their expression. Some of the natural products produced during antagonism are unknown chlorinated metabolites and deserve further study for their antimicrobial properties. In summary, this study disclosed the different responses of two Aspergillus strains in co-culture, revealed their metabolic variation, and displayed new opportunities for antibiotic discovery.

In order to improve the quality of freshwater fish surimi products, the effect of adding 4% of native cassava starch or modified cassava starch (starch phosphate, hydroxypropyl starch, acetylated distarch phosphate, or a 3:2 (m/m) mixture of acetylated distarch phosphate and hydroxypropyl starch) on improving the quality of surimi gels prepared from frozen tilapia surimi was investigated by measuring texture, rheological properties, water-holding capacity, moisture distribution and microstructure. The results showed that compared with the control group, the whiteness of tilapia surimi gels with native and modified cassava starch significantly decreased (P < 0.05), the gel strength, hardness, chewiness and water-holding capacity significantly increased (P < 0.05), the percentage of cooking loss decreased (P < 0.05), the bound water content increased (P < 0.05), and the microstructure was more uniform and compact. The best gel texture and highest water-holding capacity were achieved with the addition of the modified starch mixture. Low-field magnetic resonance imaging and optical microscopy results showed that both native and modified cassava starch could effectively keep the water in the surimi gel. The native and modified starch could absorb water and expand during the heating process, concentrating and filling the surimi gel network structure, and the surimi gel structure with the modified starch mixture was most compact and uniform. Therefore, addition of acetylated distarch phosphate-hydroxypropyl starch mixture can effectively improve the quality of tilapia surimi products, which will provide theoretical support for the development of freshwater fish surimi products.

To explore the effect of yeast-Agastache rugosus complex solution on the deodorization of tilapia, the deodorization process was optimized by single factor and response surface experiments. Gas chromatography ion mobility spectroscopy (GC-IMS) was used to identify the volatile components of tilapia meat before and after deodorization, and partial least squares discriminant analysis (OPLS-DA) was used to distinguish and analyze the differences. Results showed that when the conditions of a mass concentration of 2.1 g/100 mL, the ratio of solid to liquid was 1:3.09 (g:mL), and the deodorization time of 32 minutes, the fishy degree was the lowest and the sensory score was the highest. A total of 22 volatile compounds, mainly aldehydes and alcohols, were detected by GC-IMS. After deodorization, the relative content of aldehydes decreased from 50.64% to 40.82%, and that of alcohols decreased from 34.00% to 27.77% . According to the odor threshold value, the substances with relative odor activity value (ROAV) was greater than 1 were 1-octen-3-ol, 1-hexanol, heptanal, nonanal, octyl aldehede, ethyl acetate, and acetic acid hexyl ester. Five key fishy substances (VIP > 1) were screened by partial least squares discriminant analysis and variable importance in projection (VIP). They were octyl aldehede, nonanal, heptanal, 1-octen-3- ol, and 1-hexanol. The interaction of these substances had an important impact on the fishy smell of tilapia. [ABSTRACT FROM AUTHOR]