This work aims to evaluate the antimicrobial potential of ethanolic and water extracts of roselle (Hibiscus sabdariffa), rosemary (Rosmarinus officinalis), clove (Syzygium aromaticum), and thyme (Thymus vulgaris) on some food pathogens and spoilage microorganisms. Agar well diffusion method has been used to determine the antimicrobial activities and minimum inhibitory concentrations (MIC) of different plant extracts against Gram-positive bacteria (Bacillus cereus, Staphylococcus aureus), Gram-negative bacteria (Escherichia coli, Salmonella enteritidis, Vibrio parahaemolyticus, and Pseudomonas aeruginosa), and one fungus (Candida albicans). The extracts exhibited both antibacterial and antifungal activities against tested microorganisms. Ethanolic roselle extract showed significant antibacterial activity (P < 0.05) against all tested bacterial strains, while no inhibitory effect on Candida albicans (CA) was observed. Only the ethanolic extracts of clove and thyme showed antifungal effects against CA with inhibition zones ranging from 25.2 ± 1.4 to 15.8 ± 1.2 mm, respectively. Bacillus cereus (BC) appears to be the most sensitive strain to the aqueous extract of clove with a MIC of 0.315%. To enhance our understanding of antimicrobial activity mechanism of plant extracts, the changes in internal pH (pHint), and membrane potential were measured in Staphylococcus aureus (SA) and Escherichia coli (EC) cells after exposure to the plant extracts. The results indicated that the plant extracts significantly affected the cell membrane of Gram-positive and Gram-negative bacteria, as demonstrated by the decline in pHint as well as cell membrane hyperpolarization. In conclusion, plant extracts are of great value as natural antimicrobials and can use safely as food preservatives.

Sea Buckthorn (SB) juice is rich in biologically active compounds. It has considerable health benefits; thus, it can serve as functional food ingredient. The aim of this study was to determine and compare the total content of polyphenols, antioxidant capacity (FRAP), soluble solid content, pH value, β-carotene content and colour parameters (L*, a*, b*) in berry juice of cultivar 'Leikora' Sea Buckthorn (SB) (Hippophae rhamnoides L.). The treatment was made as control sample of Sea Buckthorn juice (C), and Sea Buckthorn juice with 0.5 % (P0.5); 1 % (P1); 2 % (P2) dried pomace of Sea Buckthorn. The samples were stored at room temperature for physicochemical analysis at interval of 2 months for a total period of 14 months.According to our results, the β-carotene (C to P2 was 3.71, 4.82, 5.49 and 6.52 mg 100mL−1) as well as the antioxidant capacity of the samples increased with the growth of the pomace content. During storage, degradation occurred in the polyphenol content and antioxidant capacity, but the β-carotene content increased. The increase of the β-carotene content was 94.6 % (C) and 32.7 % (P0.5). The smaller reduction in antioxidant compounds was the higher the sample of pomace content is. The FRAP and total polyphenol values measured during storage confirm that the pomace has antioxidant effect. There is a close correlation between the two parameters, including a positive correlation (r = 0.8614), which indicates that a significant part of the antioxidant capacity of buckthorn is due to the presence of different polyphenols.

Apple pomace contains a large amount of useful bioactive compounds that have wide application in the food industry. In this study the effect of drying temperature and pressure (high temperature 80 °C and low temperature 60 °C using a conventional oven and a combination of conventional plus vacuum drying oven) on the antioxidant capacity and phenolic compounds of apple pomace extract was investigated. For a combination of conventional and vacuum drying ovens, samples were first dried by a conventional oven to a moisture content of approximately 10% then vacuum dried to reach a final moisture content of 3–4%. After the drying processes, ethanolic extraction was performed and the amount of total polyphenol and the antioxidant capacity (FRAP) were evaluated to determine a best drying method. The drying curves were also determined. The drying temperature affects the duration of the drying, the rate of water loss, and the remaining amount of antioxidant compounds.

Food industry is searching for natural additives because consumers demand natural, safe and environmentally sound food additives. The use of different plant extracts such as grape pomace and cranberry extracts which have antimicrobial effect in food preservation has gained an increasing interest. In the latest years many researches deal with investigation of the antimicrobial effect of apple pomace extracts. Apple pomace, a residue from apple juice production, contains high amount of polyphenols which are known to have antioxidant effect. Apple pomace is a by-product of the apple juice and cider processing industry and represents about 20–35% of the original fruits. It can be used for value-added products, because it is rich in pectin, fibre, macro and micro elements and antioxidants mainly, polyphenols. Previous studies indicate that the apple pomace has high phenolic content and antioxidant activity and thus can be regarded as a valuable source of antioxidants and bioactive compounds. The contents of phenolic compounds vary greatly among different varieties of apples. Moreover, apple peels contain higher concentration of phenolic compounds compared to flesh. Conventional production of apple juice results in a juice with poor phenolic content and with only 3–10% of the antioxidant activity of the fruits that they are produced from. Thus, leaving huge amount of the phenolic compounds in the pomace. Because of this, studying extraction method for extracting high amount of polyphenol from the pomace is important. In this paper apple pomace was dried with different drying method (atmospheric and vacuum ovens, 80° C and 60°C). Extraction was performed using distilled water as solvent, and the extracts were evaluated by the colour, water soluble sugars, total polyphenol content (TPC) and antioxidant capacity.