The effect of cinnamon, oregano and thyme essential oils in marinade on the microbial shelf life of fish and meat products

Fresh and minimally processed fish and meat are easy targets for microbial spoilage. The demand for natural alternatives to synthetic additives increases. In this study essential oil (EOs) in marinades were used on fish and meat and the effect on the microbial growth during storage was assessed. EOs from Oreganum compactum (oregano), Cinnamomum zeylanicum (cinnamon), and Thymus zygis ct. Thymol (thyme) were chosen. The marinade was composed of water, Na-lactate/lactic acid buffer (2 w/w %), NaCl (10 w/w %), and EO emulsified with Tween 80 and with a pH of 4.5. The necessary Tween 80 to emulsify the EOs in the marinade depended on the EO type and was increased more than tenfold by the NaCl and lactate buffer. The treatment consisted of immersion of meat (pork filet, pork bacon, chicken filets, chicken skin), salmon or scampi for 2 min in marinade solution. The samples were stored at 4 °C in air. Samples were analyzed for microbial counts (dependent on matrix: total coliforms, Escherichia coli, lactic acid bacteria, yeasts and molds, total aerobic psychrotrophs). Growth inhibition was achieved with some EO + marinade treatments but marinade itself did not slow down the microbial growth. Most notably, the growth of yeasts and molds was inhibited by immersion of all food matrices in 1 w/w % cinnamon EO. Use of (1 w/w % for all EO) cinnamon EO (+marinade) led to microbial shelf life increase of all matrices (except the chicken matrices as the end of the shelf life was not reached during the experimental duration), oregano EO to shelf life increase of pork filet and salmon, and thyme EO of pork filet and scampi. Sensorial analysis on pork filet and salmon showed that immersion in 3% EO (resulting in 0.09 g EO/100 g pork filet and 0.05 g EO/100 g salmon) resulted in an acceptable odor after 24 h of storage. The results in this study show that the sensorial properties of the meat/fish are inevitably affected when the necessary EO concentrations to extend the microbial shelf life are applied.