Carbon dioxide is effective for extending the shelf-life of perishable foods by retarding bacterial growth. The overall effect of carbon dioxide is to increase both the lag phase and the generation time of spoilage microorganisms; however, the specific mechanism for the bacteriostatic effect is not known. Displacement of oxygen and intracellular acidification were possible mechanisms that were proposed, then discounted, by early researchers. Rapid cellular penetration and alteration of cell permeability characteristics have also been reported, but their relation to the overall mechanism is not clear. Several researchers have proposed that carbon dioxide may first be solubilized into the liquid phase of the treated tissue to form carbonic acid (H2CO3), and investigations by the authors tend to confirm this step, as well as to indicate the possible direct use of carbonic acid for retarding bacterial spoilage. Most recently, a metabolic mechanism has been studied by a number of researchers whereby carbon dioxide in the cell has negative effects on various enzymatic and biochemical pathways. The combined effect of these metabolic interferences are thought to constitute a stress on the system, and result in a slowing of the growth rate. The degree to which carbon dioxide is effective generally increases with concentration, but high levels raise the possibility of establishing conditions where pathogenic organisms such as Clostridium botulinum may survive. It is thought that such risks can be minimized with proper sanitation and temperature control, and that the commercial development of food packaging systems employing carbon dioxide will increase in the coming years.

Carbonic acid and semi-permeable packaging materials were investigated for their effect on shelflife of fresh fish. Cod fillets (Gadus morhua) were dipped in carbonic acid and then stored packaged and unpackaged at 2°C. Samples were evaluated for weight loss, surface pH, texture changes, surface microbial growth, headspace gas composition, and sensory characteristics of cooked flavor, odor, and appearance. Carbonic acid was capable of extending shelflife between 7 and 21 days; however, only at a quality level judged as fair to marginal by sensory evaluations. Low permeability packaging slowed bacterial growth and extended shelflife, but retained off-odors and established low oxygen conditions which may present a risk from the growth of pathogenic organisms.

Agricultural technology has increased crop yield potentials, but on rain‐fed crops yields are still severely reduced with the normal climatic frequency of drought. Objectives were (1) to determine an interaction regression of county average corn (Zea mays L.) yield on a soil moisture stress variable and technology trend and (2) to estimate the probability of soil moisture stress and resulting average corn yield in Tippecanoe County, Indiana. The soil moisture stress variable (Sc) was the sum of modeled daily ratios of actual to potential evapotranspiration [Σ(ET/PET)] over critical corn growth and development periods. The interaction regression model of corn yield on Sc andyield on Sc andyield on Sc andyield on Sc and technology trend (T = year) for Tippecanoe County was associated with 70% of the variance in the 1961 to 1992 average county corn yields when Sc was a 90‐d period (S90) from 39 d before corn silking to 50 d after. With no moisture stress (S90 = 90), the technology trend over the last 32 yr was 0.17 t ha−1 yr−1 (2.7 bu acre−1 yr−1). With 1992 technology, each deficit unit of S90 reduced the yield 0.19 t ha−1 (3.1 bu acre−1). The distributions of S90 and predicted corn yield were highly negatively skewed. The probability of having an S90 less than 85 (at least some moisture stress), and a county corn yield less than 9.5 t ha−1 (152 bu acre−1) is 69%, but the probability of severe stress (S90 < 75) and corn yield less than 7.5 ± 0.8 t ha−1 (139 ± 13 bu acre−1) is 22%. For the same weather regime, the probability of moisture stress and resulting corn yields differs greatly for individual soils. For a poorly drained soil (Typic Argiaquoll) the probability of having an S90 less than 85 is 41%, but for a well‐drained soil (Typic Argiudoll) the probability is 90%.