Evaluation of the Inhibitory Effectiveness of Some Citrus Peel Tannins on the Microbial and Chemical Content of Minced Beef During Cold Storage at 4°C

The present study aimed to evaluate the inhibitory efficiency of aqueous extract tannins from four types of citrus peels (orange, lemon, grapefruit, and bitter orange) at two concentrations (0.25% and 0.5%) in reducing bacterial counts and chemical changes in minced beef stored at 4°C for 10 days, compared to a control treatment. The results revealed a significant effect ( p < 0.05 ) for all extracts, leading to a reduction in bacterial growth compared to the control group, which exhibited the highest bacterial load on day 10 ( 9.8 log CFU/g). The oxidative rancidity test revealed a significant increase that led to the spoilage of the control treatment due to severe oxidation, with the rancidity value reaching 2.90\ {mg MDA/kg} on the tenth day, while the pH value rose to 8.25 by the same day as a result of protein degradation and the release of volatile nitrogenous compounds. The results demonstrated the significant superiority of orange peel extract at a 0.5% concentration as an antioxidant and antibacterial agent throughout the storage period; it recorded the lowest total bacterial count on the tenth day at 6.85 log/g and the lowest oxidative rancidity value, averaging 0.40 mg MDA/kg. Meanwhile, bitter orange peel extract at 0.5% exhibited high synergistic efficacy, particularly in stabilizing the medium's acidity and preventing meat alkalinity, achieving the lowest pH value of 5.55 on day ten. This effectiveness of the extracts especially orange and bitter orange is attributed to their high content of tannins and phenolic compounds, which function as natural free radical scavengers and metal ion chelators, in addition to their capacity to form stable complexes with proteins that inhibit bacterial degrading enzymes. The study concludes that citrus peel tannins (particularly orange and bitter orange) can be applied as safe, effective natural alternatives to synthetic preservatives, extending the shelf life of refrigerated meat and supporting environmental sustainability through the recycling of agricultural waste.