Lipid stability of dehydrated beef strips stored in two packaging types

Meat is an excellent source of many essential nutrients and makes an important contribution to a balanced diet. Vacuum frying is the technique of deep frying foods under vacuum, and is essentially a dehydration process that develops the desirable sensory properties of traditional fried foods. Vacuum frying has been demonstrated to great effect on fruits and vegetables, but has been used only rarely with animal products and, until now, not with beef. In this study, strips of marinated beef were vacuum fried and stored in two different packaging materials in order to determine the effects on lipid quality of packaging and storage. The packaging types were polyethylene terephthalate (PET) and aluminium foil laminate. Vacuum fried beef samples were stored at 11°C, 15°C, 25°C, 35°C and 39°C for 3, 5, 10, 15 and 17 weeks and the samples and extracted oil was analysed. Response surface methodology (RSM) was used to analyse the responses and the equations generated were also used to predict responses during storage up to 32 weeks at 15, 20 and 25°C. Moisture content and water activity (aw) were only affected following storage in PET packaging. Lipid decomposition was evidenced by significant increases in free fatty acids (FFAs) for both packaging types and Totox value with PET packaging, though these changes were considered to be minor with FFAs reaching only 4.0 (% oleic acid) during 17 weeks of storage and predicted to increase to over 8% after 32 weeks of storage and Totox value not exceeding 32 even after 32 weeks of storage. There were no significant changes in the unsaturated fatty acid content but the levels of polyunsaturated fatty acids, linoleic and linolenic acids decreased during 17 weeks of storage, and average levels were higher in the aluminium foil packaging, indicating that less oxidation had occurred. The tocopherol content decreased significantly from initial concentrations and mean levels were higher in the oil from vacuum fried beef strips stored in aluminium foil laminate packaging, but the response could not be satisfactorily modelled by RSM. Sterol oxidation products (SOPs) were also measured but were unable to be modelled, although higher average levels were found in the oil from vacuum fried beef strips stored in PET packaging. The results of this experiment suggest that vacuum fried beef strips can be stored for up to 32 weeks at temperatures 15-25°C without significant lipid deterioration. Aluminium foil laminate packaging reduced most of the changes that occurred due to lower oxygen and water vapour transmission rates. Future research into the shelf-life of vacuum fried beef strips should concentrate on the use of antioxidants to reduce oxidative changes, SOPs formation and a sensory analysis to determine the acceptability of the products after storage

Effects of UV-B radiation on oxalate content of silver beet leaves

Silver beet (Beta vulgaricus var. cicla) a common vegetable in New Zealand is known to contain high levels of oxalates in the leaves. Silver beet plants were grown in a field trial under glass and perspex sheets which filtered sunlight reaching the plants. After eight weeks of growth, the plants were harvested and the total, soluble and insoluble oxalate content of the leaves of the plants grown under the two filter treatments and a no-frame control were measured. Perspex allowed the transmission of UV-A, UV-B and photosynthetically active radiation (PAR), whereas glass excluded UV-B radiation. No significant differences between the perspex treatment and the no-frame control were observed when the data was compared on a wet matter (WM) or dry matter (DM) basis. Shielding the growing plants with glass significantly reduced the total oxalate and soluble oxalates to 83 and 84% respectively when compared to the perspex and no-frame treatments

Vacuum fried gold Kiwifruit: Effects of frying process and pre-treatment on the physico-chemical and nutritional qualities

A study was conducted to determine the effects of frying process and pre-treatment on the physico-chemical and nutritional qualities of vacuum fried gold kiwifruit. The kiwifruit samples were peeled and cut into slices 5 mm thick. Half of the kiwifruit samples were soaked for one hour in a 33% maltodextrin solution, then placed into plastic bags and frozen and the other half (unsoaked) were simply frozen. The two set of samples were subjected to three frying processes and all at 2.3 kPa vacuum, after which the kiwifruit was removed from the fryer and centrifuged in cheese cloth for four minutes to remove excess surface oil. Generally, the vacuum fried gold kiwifruit samples from the 80°C for 50 minutes process gave higher moisture content and lower oil content followed by the samples from the 90°C for 35 minutes process and then the 100°C for 25 minutes process. The vacuum fried samples from the 100°C for 25 minutes process gave consistently higher total colour change and browning index, followed by the 90°C for 35 minutes process and then the 80°C for 50 minutes process. The unsoaked sample from the 80°C for 50 minutes process gave significantly lower breaking force than the sample from the 100°C for 25 minutes process. There was no significant difference in the breaking force of all vacuum fried soaked samples. Generally the samples from the 80°C for 50 minutes process gave higher ascorbic acid contents followed by the samples from the 90°C for 35 minutes process and then the 100°C for 25 minutes process. © 2011