B. Ooraikul

Novel approach to oxygen control in modified atmosphere packaging of bakery products

PDA plates inoculated with mould spores were packaged in air and in a mixture of CO2N2 (60 : 40) with headspace oxygen adjusted to range from <0·05% to 10% (vv) and stored at 25°C. Those packaged in air showed mould growth after 1–1·5 d, while those in the gas mixture showed growth between 4–6 d after headspace oxygen reached a minimum concentration of 0·4%. Uninoculated plates packaged in air showed no change in headspace oxygen concentration over 30 d at 25°C, while those in the gas mixture with initial headspace oxygen of <0·05% showed a steady increase of oxygen, through packaging film permeability, at an average rate of 0·06%/d. If uninoculated plates were packaged in air together with a sachet of oxygen absorbant called Ageless, the headspace oxygen was quickly reduced to <0·05% within 9 h and remained unchanged thereafter. Crusty rolls with aw of 0·95 and pH of 5·62 developed mould after 5–6 d when packaged in air, 9–11 d in 100% N2 and 16–18 d in CO2N2 (60 : 40). However, when Ageless was incorporated into all the packages the product remained mould free for >60 d. This study shows that oxygen absorbants offer the bakery industry a viable alternative to gas flushing.

Shelf life extension of a bakery product using ethanol vapor

Studies to determine the effect of ethanol vapor on growth of Saccharomyces cerevisiae , the spoilage isolate of gas packaged apple turnovers were undertaken. Ethanol vapor was generated from a commercially available preparation Ethicap which releases a controlled amount of ethanol vapor into package headspace. The effectiveness of ethanol vapor against S. cerevisiae in an agar model system was a function of a w of test medium and concentration of ethanol vapor. While a reduction of a w alone failed to inhibit growth of S. cevevisiae , growth was completely suppressed at a w 0·9 and 1·52% (v/v) ethanol vapor and at a w 0·85 and 0·56% or 1·1% ethanol vapor. Apple turnovers, with a w of 0·93 and pH of 5 had a shelf life of 14 d when packaged in air or a CO 2 : N 2 (60 : 40) gas mixture and stored at ambient temperature. Packages were visibly swollen due to growth of S. cerevisiae and additional CO 2 production. However, when Ethicap was incorporated into packaged product, yeast growth was completely suppressed and all packages appeared normal at the end of the 21d storage period. This study has demonstrated the usefulness of ethanol vapor for shelf life extension of a fruit filled bakery product.

Use of response surface methodology in shelf life extension studies of a bakery product

Abstract Effects of water activity, pH, storage temperature, concentration of potassium sorbate, CO2 concentration in the package headspace and inoculum level on growth of Aspergillus niger, the major spoilage isolate of English style crumpets, was studied on an agar model system using an experimental design termed Response Surface Methodology. The initial screening design indicated that aw, pH, levels of potassium sorbate, CO2 and storage temperature were significant variables. When a central composite rotatable design was subsequently applied to four variables with pH held constant at pH 6.5 only aw, storage temperature and CO2 level were found to have a significant effect on mold growth. Using multiple regression analysis, a second order polynomial model was derived and used to predict the number of days to visible mold growth under various combinations of the remaining three variables. Generation of contour plots enabled selection of levels for each variable to give a product with a desired mold free shelf life. Typically, crumpets with an aw of 0.96, packaged in 62% CO2 had a mold free shelf life of 20 d when stored at 20°C. The observed shelf life results agreed well with predicted values on Potato Dextrose Agar and demonstrated RSM as a powerful and elegant research tool when several variables are to be evaluated simultaneously.

Control of fermentation problems in a gas packaged bakery product using a Response Surface Methodology approach.

Abstract English style crumpets of aw 0·98 and pH of 6·0 were packaged in a CO2:N2 (60:40) gas mixture, stored at 25°C and 30°C monitored for changes in package volume. For packages stored at 25°C, package volume decreased during the initial storage period. Subsequent in-package C02 production resulted in all packages having a blown appearance when a critical volume of 1700 ml was reached after 16–20 days storage at 30°C and 25°C respectively. Effects of water activity (aw), pH, storage temperature, concentration of potassium sorbate, C02: air ratio and inoculum level on the growth of, and C02 production byLeuconostoc mesenteroides, the major spoilage isolate of gas packaged crumpets, were studied in agar and broth model systems using an experimental design termed Response Surface Methodology (RSM). The preliminary screening design indicated that aw, pH and storage temperature were the most significant variables influencing growth ofL. mesenteroides in an agar model system. Further study to evaluate the effects of the three variables on C02 production byL. mesenteroides in a broth model system generated a second order polynomial equation which was used to predict levels of C02 production under various combinations of these variables. Based on this and previous studies, it was found that crumpets reformulated to aw 0·965–0·97 and pH 5·25–7·25 and packaged in 60% C02 could be stored at ambient temperature for 25–30 days without visible mold growth, or C02 production and swelling of packages. This study demonstrated RSM as a powerful and useful research tool when several variables are to be studied simultaneously.