Original research article
Effect of Rosemary and Oregano Aqueous Extracts Supplementation on Microbial Growth during Refrigerated Storage of Milk
2023, 88 (1) p. 67-73
Asma SERRER, Abdelhafid BOUBENDIR, Khadidja BOUCHAIR, Saber BOUTELLAA
Abstract
The aim of the present study is to evaluate the effect of adding rosemary and oregano aqueous extracts to raw cow milk on the dynamics of microbial growth during milk refrigeration. The aqueous extracts from plants leaves were prepared and supplemented to milk samples at different concentrations: 0, 0.25, 0.5, 0.75 and 1 mg mL-1 for rosemary and 0, 1.25, 2.5, 3.75, 5 mg mL-1 for oregano. The evolution of microbial growth was monitored at regular intervals of times during ten days of refrigerated storage at 4 °C. The enumeration of the microbial flora was conducted by the culture methods. The supplementation of the two plants extracts to refrigerated milk generated a prolongation of the lag phase duration and limited microbial growth. For rosemary, the lag phase length (λ) in milks without supplementation (0 mg mL-1) was prolonged from 1.2 ± 0.80 day (28.8 h) to 1.66 ± 0.92 day (39.84 h) in milks added with 0.75 and 1 mg mL-1 while the maximum cell load (Xmax) diminished from 7.00 ± 0.17 log CFU mL-1 in non-supplemented milks to 6.56 ± 0.19 log CFU mL-1 in milks added with the same concentrations. For oregano, λ was delayed from 4.12 ± 0.11 day (98.88 h) in milks without supplementation to 5.04 ± 0.97 day (120.96 h) in milks added with 1.25 mg mL-1. A decrease of Xmax was remarked for the whole of the concentrations, registering the lowest value of 4.45 ± 1.34 log CFU mL-1 at 2.5 and 3.75 mg mL-1. The use of rosemary and oregano aqueous extracts as natural additives during refrigeration could offer opportunities as biopreservatives in the milk industry, to reduce heat pretreatment and the addition of chemical additives.
Keywords
biopreservatives, cold storage, microbial dynamics, plants extracts, psychrotrophic bacteria
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