Application of essential oils to prolong the shelf-life of the pre-cooked Asian noodle - Hokkien noodle : a case study of the systematic design approach : a thesis presented in partial fulfilment of the requirements for the degree of Master of Food Technology, School of Food and Advanced Technology, Massey University, Albany, New Zealand
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Date
2020
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Massey University
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Abstract
Asian noodle is one of the traditional staple foods with a long history in the Asian regions. There are several varieties of Asian noodles which are now consumed worldwide by different ethnic groups. One of the popular noodle products commonly found in New Zealand (NZ) is the pre-cooked Asian noodle, such as the Hokkien noodle. Typically, the Hokkien noodle is yellowish with a chewy texture and characteristic taste. The shelf-life of the pre-cooked Hokkien noodle ranges from a few days to less than a fortnight at 4°C, but this depends on the efficiency of packaging and storage conditions as well as the manufacturing environment. The main challenge affecting the shelf-life of pre-cooked noodles is microbial spoilage. The current study investigated the potential of using essential oils (EOs) to improve the shelf-life of the pre-cooked Hokkien noodles sold in NZ. The study comprised of three stages: the selection of EOs with antimicrobial properties; modelling the ratio of two selected EOs for formulation design; and evaluating the effect of the optimum formulation of the EOs on the storage stability of the Hokkien noodle. In stage one, the broth micro-dilution and the agar disc diffusion methods were used to select potential EOs with high antibacterial and/or antifungal properties. Clove and oregano essential oil showed the best inhibitory effects against fungi and bacteria, respectively. In stage two, the experimental mixture design was used to determine the optimum combination of the two EOs for developing the final formulations. The designed model included the regulated national limits for the standard plate count (SPC) and yeasts and moulds count (YMC). Overall consumer sensory acceptance of the products was also evaluated by the 9-point hedonic scale. The model predicted that 2.72% of oregano EO combined with 10.91% of clove EO (in the presence of 86.37% soybean oil) could provide 1.72 and 0.9 log CFU/g reductions on bacteria and fungi counts compared with the control sample, respectively. The overall consumer acceptability of EOs-added Hokkien noodle was predicted at 68.03%. The final phase investigated the shelf stability of the Hokkien noodle treated with the optimum combination of clove and oregano EOs for 65 days. The prepared noodles were packaged under MAP condition (N₂:CO₂ = 70:30) and storage at 4˚C. Samples of Hokkien noodle treated with the essential oils were analysed for SPC and YMC. Water activity, pH, colour and texture were also measured. The microbial counts (SPC and YMC) of the experimental samples and the control did not exceed the regulated national limits (6 log CFU/g & 4 log CFU/g, respectively) throughout the experimental period. Control samples contained 4.16 log CFU/g of SPC and 1.96 log CFU/g of YMC by the end of the study. By using the Baranyi-Robert predictive model, the shelf-life of the control samples were estimated to be around 81 days/4°C. For the EO-coated samples, SPC decreased to ≈1 log CFU/g and stabilised until the end of the experiment, while fungi were recorded at <1 log CFU/g. The shelf-life of the EOs-treated Hokkien noodle was calculated to be least 22 days more than the control, thus was achieving over 100-days. It was also shown that additional EOs did not affect other parameters (pH, Aw, colour, texture) of the Hokkien noodle (p≥0.05). For future studies, using active packaging technology to deliver EOs to the product is recommended, which may increase consumer acceptability.
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Asian noodle, shelf-life, oregano, clove, essential oil, antimicrobial, mixture design, modelling