Modified atmosphere packaging was investigated as a preservation technique for tofu. Tofu was packaged in air (control) and in 30% carbon dioxide (CO2)/70% nitrogen (N2), accomplished through flushing or vacuum compensation, and stored in refrigerated conditions. During storage, oxygen and carbon dioxide concentrations were monitored in the packaging headspace, and microbial numbers in the tofu were assessed. Substantial amounts of oxygen (O2) were deliberated from the tofu during storage, and CO2 was absorbed into the product. Pronounced changes in gas profiles clearly coincided with rapid microbial growth. At 10 days of storage, microbial counts were 1 to 4 log cycles higher in air-packaged tofu compared with tofu packaged in modified atmosphere. At 3 weeks of storage, the counts in modified atmosphere-packaged tofu reached the same level as those in air-packaged tofu. Modified atmosphere packaging as applied in this study was demonstrated to retard microbial growth up to 14 days. PRACTICAL APPLICATIONSTofu is produced globally in large quantities, but it is highly perishable. This is the first report on the application of modified atmosphere packaging (MAP) for tofu. Our research demonstrates (1) that microbial growth can be retarded by packaging tofu in 30% CO2/70% N2; and (2) that the application of MAP to a food product can be evaluated by repetitive monitoring of O2 and CO2 concentrations in the headspace during storage. For tofu, the O2 and CO2 profiles reveal substantial gas exchanges between product (and its microflora) and headspace. For fresh fruits and vegetables, evolutions in the headspace gas composition during storage due to respiratory activity are known and taken into account in the design of a MAP application. Our findings point out that also for non-respiring products, gas composition changes should be anticipated when developing a MAP application.

Aims:  The objective was to study the growth of Pseudomonas in a food product (tofu) where it typically occurs as a spoilage organism, and when this product is stored under modified atmosphere. Methods and Results:  A Pseudomonas strain was isolated from the endogenous microflora of tofu. Tofu was inoculated with the strain, packaged in different gas conditions (air, 100% N2, 30% CO2/70% N2 or 100% CO2) and stored under refrigerated conditions. Microbial loads and the headspace gas composition were monitored during storage. Conclusions:  The strain was capable of growing in atmospheres containing no or limited amounts of oxygen and increased amounts of carbon dioxide. Even when 100% CO2 was used, growth could not be inhibited completely. Significance and Impact of Study:  In contrast to the general characteristics of the genus Pseudomonas (strictly aerobic, highly sensitive to CO2), it should not be expected in the food industry that removing oxygen from the food package and increasing the carbon dioxide content, combined with cold storage, will easily avoid spoilage by Pseudomonas species. Guarantee of hygienic standards and combination of strategies with other microbial growth inhibiting measures should be implemented.