Food Shelf Life

"Beer is highly susceptible to light, and we might add, light from any source. In sunlight, the reaction is almost immediate. The ultraviolet part of the light spectrum breaks down the sulphur containing molecules, forming highly odourous mercaptans and other sulphurous compounds. A customer complaint on this subject cannot possibly be mistaken, as a most objectionable odour and flavour is present."

"A surprising fact is that beer in the regular amber bottle will begin to be noticeably 'lightstruck' within about two minutes, while beer in a clear glass will begin deteriorating within 30 seconds!"

"It is well known that milk, if exposed to either sunlight or artificial light (i.e., fluorescent lighting found in most dairy cases), can develop flavor changes and nutrient losses, especially of riboflavin (vitamin B2), vitamin A (particularly added vitamin A), vitamin C (which is present in low quantities in milk), and added vitamin D."

"The extent of flavor changes and nutrient losses depends on several variables. Among these are the light intensity, illuminance and wavelength, the distance between the light source and milk container, container material, amount exposed surface area, surface to volume ratio, temperature, and duration of exposure."

"In terms of nutrition, loss of riboflavin is directly related to the amount of ultraviolet light transmitted through the container."

"Vitamin C or ascorbic acid is particularly light-sensitive. In milk, the rate of destruction of vitamin C is proportional to the amount of light transmitted through the container."

"In a study in Pennsylvania, almost half of 449 samples of milk in translucent plastic jugs were reported to have developed pronounced light-induced off-flavors within 36 hours."

"Light-oxidized defect develops in milk as a result of its exposure to sunlight or to fluorescent lighting (wavelengths below 620 nm) common in store dairy cases. Light initiates a chemical reaction in milk that modifies specific proteins and fats, resulting in the characteristic off-flavors. Certain vitamins (i.e. riboflavin and vitamin A) are also susceptible to light-induced degradation in a similar manner."

"Exposure to sunlight for as little as 10-15 minutes (5 minutes in very intense light) is sufficient to cause the defect, while longer exposure times are generally required for fluorescent lighting. The closer the milk is to the fluorescent light source (or the more intense the light), the quicker the development of the off-flavor.

"In general, the defect is more common in milk packaged in transparent glass or plastic, though it can also occur in milk in paper cartons if there is sufficient light intensity and exposure time."

"Today's consumers are very demanding and quality driven, they have learned through experience that the desirable color of fresh/ground beef is bright cherry-red, and any deviation from what they perceive to be acceptable will not be purchased. Retailers discount or discard cuts that have color characteristics outside the marketable range resulting in economic losses to the company."

"Current estimates are that the value loss of fresh beef due to discoloration costs the retail beef industry 4 to 5 percent of the wholesale price or up to one billion dollars a year (Hoffman-La Roche Inc., 1993). Beef that is perfectly wholesome and safe to eat is discounted or thrown away every day because it has lost its bloom, or cherry red color, and become visually unappealing to consumers (Westcott et al.,1997)."

"Since cold-tolerant bacteria capable of spoiling meat continue to grow to at least -3° C, their growth on unfrozen meat can not be prevented and as the meat temperature increases the growth rate of the bacteria also increases."

"Increasing the storage temperature by only a degree or two has a profound effect on product storage life in any type of preservative packaging utilized. Therefore, any temperature increase, above the optimum, produces a proportional decrease in storage life. For example, storage at commercial (2° C), as opposed to optimum (-1.5° C) temperatures reduces product storage life by 50% (Gill and Shand, 1993)."

"In addition, surveys of retail outlets have shown product surface temperatures to be 4 to 25° C higher than the temperature of the retail case (Holland, 1979), and a product surface temperature of 10° C was not uncommon under retail conditions (Greer, 1984)."

“The retail case life of fresh beef is usually limited to 2 to 3 days due to the development of undesirable surface discoloration. This reduction in color acceptability has been shown to be related to the growth of psychrotrophic bacteria at the meat surface. The retailer can improve the keeping quality of beef by reducing the number of bacteria initially contaminating the meat and by controlling the growth of organisms which are present.”

“In view of the importance of color to beef acceptability, the extent of bacterial-induced surface discoloration can be used as a measure of retail beef case life. As bacteria grow on the meat surface they accelerate the oxidation of meat pigments which results in a progressive deterioration of the acceptable red color and the appearance of varying degrees of brown surface discoloration until the steak is completely discolored.”

“The growth rate of a typical beef spoilage bacteria can double as the temperature of incubation increases from 1 to 5° C and can triple with a further increase to 10° C. Increased bacterial growth means reduced case life.”

“The actual surface temperature of steaks on retail display is much higher than that recorded at the blower thermometer. In this particular case, the blower thermometer indicated a temperature of -0.5° C while displayed steak surface temperatures were on the average about 8° C higher (7.3° C).”

“Another important consideration is the intensity and duration of display illumination. The display case in the studies described herein was illuminated with 150 watt incandescent, cool-beam floodlights to give a light intensity of about 80 foot-candles at the meat surface. Lighting was automatically timed to illuminate the display case for 12 hours/day."

"During this 12 hour period of illumination steak surface temperatures were found to be higher than in the absence of illumination. This is a type of ‘greenhouse effect’ in that the heat produced by radiant energy is absorbed by the meat and trapped between the polyvinyl wrap and the meat surface. Thus, although display illumination enhances the appearance of beef it is detrimental to keeping quality."

"A survey by Food Marketing Institute revealed a strong correlation between display size and shrinkage. Stores with long full-service seafood case frontages indicated an overall shrinkage rate of 15 percent while those with small departments experienced just 5 percent. Interestingly, the reverse was true for self-service operations."

"As fresh seafoods lose quality they also lose their ability to hold water, accelerating drip loss. This is readily apparent in oyster meats but is equally true in other shellfish and finfish. Drip and dehydration may be substantial. Cooked shrimp may lose 15 percent of their weight within three days and raw shrimp considerably more. Fish fillets and steaks are very vulnerable to drip, and the amount for one species may be double that of another.”

"Texas A & M specialists have observed that the air just two inches above a bed of ice in an unrefrigerated case may be at room temperature. Similarly, researchers at Virginia Tech have recorded as much as a 25° F difference between the bottom and top of a stack of flounder fillets piled on ice. Obviously this is not acceptable."

"Fluorescent lighting in retail dairy display cases induces vitamin A degradation and 'light-oxidized' flavor defects in milk products packaged in light-transmissible (i.e. high-density polyethylene - HDPE) containers."

"Based on the results of this study, trained panelists were able to detect oxidized flavor after 15 to 30 minutes of light exposure while consumers required between 54 minutes and 2 hours."

"Ice cream contains a high percentage of fat compared with other food products; therefore, ice cream might deteriorate during storage under strong lighting in grocery stores. Light-induced oxidation could potentially cause serious problems in the quality and safety of ice cream."

"Hops help flavor beer, inhibit bacterial growth and are largely responsible for the stability of the foam in the head," Forbes said. "Hops, however, are light-sensitive, and the three main compounds in them identified as being light-sensitive are called isohumulones. When attacked by either visible or ultraviolet light, these break down to make reactive intermediates known as free radicals that lead to the offensive taste and skunky odor."

Light is one of the major factors responsible for the deterioration of fresh and dehydrated produce.

When fruits and vegetables are processed and stored, their quality is compromised by lipid oxidation, a chemical reaction that affects the color, flavor, odor, and nutritional value of the food.

If factors such as exposure to light and heat are controlled, the rate of photo-oxidation can be reduced and nutrient loss can be prevented.

"Greening is strongly affected by the cumulative effects of light quality, duration, and intensity."

"As a rule, fluorescent light above 75 foot-candles exposure at room temperature (68°F) for three to five days will start the greening process; however, light intensity as low as 5 foot-candles and light durations as short as 12 hours can cause greening of a few potato varieties such as Kennebec."

"In potato tubers, the greening is a sign that there may be an increase in the presence of glycoalkaloids, especially the substance solanine."

"Unlike chlorophyll, light is not needed for solanine formation, but, with light, glycoalkaloid formation is increased."

"When potato tubers are exposed to light, the solanine content in the peel may increase as much as ten times. Toxic levels for people are about one-hundredth of an ounce for a 200-lb person."

"But, with UV light-exposed whole tubers in which solanine had increased ten-fold, only two pounds could cause a reaction. Potentially high levels for a 100-lb and 50-lb person would be 16 and 8 ounces of a fully green potato, respectively."

"Potatoes containing more than 0.1 percent solanine (.01 oz / 10 oz potato) are considered unfit for eating."

"It is a less commonly known fact that potatoes produce compounds called glycoalkaloids that have been shown to be toxic to both man and to animals."

"At high enough levels the glycoalkaloid found in potatoes known as solanine can cause irritation of the gastrointestinal tract, impairment of the nervous system, and it is believed that they can cause teratogenic or birth defects. Neurological signs can include ataxia, convulsions, coma, muscle weakness, and involuntary urination."

"The critical part for beer skunking seems to be wavelengths shorter than about 500nm."

"Note that the brown bottles transmit a lot less light in this part of the spectrum than do the green and clear bottles."

"One way to have good-tasting milk is to protect it from light."

"Both natural and artificial light can induce quality defects that consumers notice -- and don't like. Light exposure causes chemical reactions in milk that can modify the proteins and fats that are present to produce many negative flavors, ranging from burnt protein (burnt feathers or hair) to cardboard or metallic. The resulting off-flavors are dependent upon various factors such as exposure time, intensity and wavelength of light, and composition of the milk."

"Meat spoilage is a significant concern for the Canadian beef industry, with related costs estimated at $200 million per year."

"Previous research has shown that lactic acid bacteria are the primary bacteria in vacuum-packaged meat and that with extended refrigerated storage, their numbers attain high levels and spoilage ensues. Currently, vacuum packaging is used to market about 80 percent of Canadian beef to domestic and international markets."

"The fact that foods are diverse, complex and active systems, in which microbiological, chemical, enzymatic and physicochemical reactions can simultaneously take place, evaluating shelf life is an arduous task."

"Maintenance of quality and safety is dependent on the understanding of these reactions, the influence of the environment and the successful limitation of the ones most responsible for spoilage or loss of desirable characteristics."

"Exposure to light causes potato tubers to green, due to the conversion of amyloplasts to chloroplasts, and accumulate toxic steroidal glycoalkaloids. The two major alkaloids, comprising 95% of the total (TGA), are a-solanine and a-chaconine. The consumption of potatoes with high TGA concentrations can cause illness and even death."

"Glycoalkaloids are toxic to humans; the lethal dose is considered to be 3-6 mg per kg body mass."

"On exposure to light the potato tuber will produce elevated levels of these protective glycoalkaloids, with the highest levels being in the sprouts as they emerge from the tuber."

"In a recent paper delivered at a Pediatrics Congress (Symposium of Congential Malformations) held in Barquisimeto-Lara, Venezuela, Ruben Dario Cortez said that there is a relationship between the consumption of damaged and green potatoes, and neural tube defects."

"The concern with greened potatoes should not be the color but the fact that solanine, a potentially toxic alkaloid, develops in the same area along with the chlorophyll. Greened potatoes, therefore, are often higher in solanine than those not greened. The bitter taste associated with greened potatoes is caused by the solanine, not the chlorophyll."

"Potatoes also develop more greening under light exposure, when temperatures are higher, e.g., 68 °F versus 41 °F. Retail packaging can also contribute to increased greening. Consumers want to be able to view produce prior to purchase. Packaging materials have changed over time from burlap and other opaque materials to transparent bags which allow exposure to light during retail storage and display."

"The green indicates an increase in the presence of glycoalkaloids, especially, in potato, the substance 'solanine' (see structure). When the potato greens, solanine increases to potentially dangerous levels."

"Unlike chlorophyll, light is not needed for solanine formation but is substantially promoted by it."

"As a rule, fluorescent light above 75 foot-candles exposure at room temperature, 68F, for three to five days will start the greening process. Light intensity may be as low as 5 foot-candles and light durations as short as 12 hours can cause greening of a few potato varieties such as Kennebec."

"The last decade has seen an exponential increase in the consumer demand for poultry and poultry products, fueled in part by dietary health considerations."

Consumers have "fears over microbiological food safety issues, especially the incidence of Salmonella spp. and Campylobacter spp."

"Muscle foods, such as meat and poultry, are described as spoiled if organoleptic changes make them unacceptable to the consumer. These organoleptic characteristics may include changes in appearance (discoloration), the development of off odors, slime formation, changes in taste, or any other characteristic which makes the food undesirable for consumption. While endogenous enzymatic activity within muscle tissue postmortem can contribute to changes during storage, it is generally accepted that detectable organoleptic spoilage is a result of decomposition and the formation of metabolites caused by the growth of microorganisms."

"The best storage tanks are made of materials to protect the oil from air and light, and are kept at relatively constant temperatures."

"When a consumer is presented with a package of fresh meat, visual appearance is rapidly assessed and is interpreted into a response: to buy or not to buy, to eat or not to eat."

"Color is probably the single most important appearance factor, especially today when meat cuts are already packaged. Packaged meat makes the consumer less able to get a true sense of smell and touch, which could be used to evaluate factors such as tenderness, juiciness, and flavor."