Pasteurization radiation offers a new means of extending the refrigerated storage life of foods. This procedure avoids many of the undesirable changes which result when sterilization radiation is used and still eliminates most of the spoilage organisms. Shrimp was treated with 5 ppm chlortetracycline and subjected to pasteurization levels of gamma radiation and stored at 38°F. The levels of irradiation used were 0.5 and 0.75 megarad. These levels were based on the flavor threshold of irradiation intensity. The quality of the stored irradiated shrimp was determined by subjective evaluation, chemical analyses and microbiological examinations. The storage life of the shrimp irradiated at 0.5 megarad was extended to 5 weeks, compared with 1 week for the unirradiated samples held at the same temperature. Throughout the ten week storage period, the samples which received doses of 0.5 megarad and CTC and those which received 0.75 megarad with and without CTC remained in good condition. / Graduation date: 1963

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M.Sc. (Chemistry) / Please refer to full text to view abstract

Graduation date: 1961

Graduation date: 1961

Chicken breast muscles (Pectoralis major and Pectoralis minor) were subjected to low doses of gamma radiation (≤ 0.50 Mrad) within 20-30 min. post-slaughter. pH decline extractability of different muscle protein fractions, shear force, isometric tension pattern and sarcomere length were evaluated at definite intervals of post mortem storage period. pH measurements from 1/2 hour to 72 hours post mortem revealed a stimulation of pH decline immediately after irradiation in 0.25 and 0.50 Mrad treated muscle samples but this effect was subsequently found to be nullified and an ultimate pH of about 5.55 was reached between 6-12 hours in all the samples. Extractability of total soluble and total myofibrillar proteins of muscle increased with post mortem time. A clear effect of irradiation treatments of increased extractability of actomyosin especially in the post rigor period was observed and this effect was more noticeable in 0.50 Mrad than in 0.25 Mrad samples. Comparatively less extractable actomyosin was found during the post rigor period of storage particularly in control samples. There was no significant effect of radiation doses, time of storage or their interactions on the solubility of sarcoplasmic proteins or of four minor fractions of protein and non-protein substances. The level of extractable actomyosin was found to be significantly related (r² = 0.12; df=46) with the corresponding shear press measurements. Irradiated samples had significantly higher mean shear values and more extractable actomyosin than the control samples especially during the post rigor period. Irradiation (0.125 and 0. 250 Mrad) was found to stimulate post mortem development of isometric tension in muscle strips. In irradiated samples maximum tension was developed about 2 hours ahead of the corresponding controls. A 50% decline of isometric tension was achieved in 6-8 hours post mortem, while a 50% decline of tension in control samples required more than 12 hours. The general relationship of isometric tension pattern and extractability of actomyosin was found to be low. Sarcomere length was related (r² = .38; df = 6) with shear values such that a small change in sarcomere length was found to result in a relatively large change in shear press values. Irradiated samples with relatively shorter sarcomeres in the post rigor period were found to have significantly lower mean shear values when compared with their respective control samples. / Land and Food Systems, Faculty of / Graduate

The total water uptake, rate of water uptake, extract release volume and maximum shear force were measured on a series of samples of irradiated freeze-dried beef. Forty seven pieces of round steak (2.5 cm x 2.5 cm x 10.4 cm or 1" x 1" x 4") were irradiated at one, three and five megarad. The control samples were not irradiated. Half of the samples were irradiated when fresh, and the other half were irradiated after freeze drying. This procedure has been defined as the "fresh-dry" irradiation sequence throughout the report. The samples were frozen in an air blast at two temperatures (-22.2°C and -56.1°C). Freeze-drying was carried out below 300 microns of Hg and a maximum shelf temperature of 15.6°C (60°F). There appears to be three phases of water uptake: 1) A very rapid, almost instantaneous, absorption. 2) A more gradual uptake (called Part.1 in the report). 3) A relatively slow asymptotic approach to an equilibrium condition (Part 2). These two last phases are shown to be straight lines when the logarithm of the water uptake is plotted against the logarithm of the immersion time. Irradiation level has no significant effect on the final water content or on the slow asymptotic absorption (Part 2) or the extract release volume, but has a significant effect on the gradual water uptake (Part 1) and on the shear press force. Fresh-dry irradiation sequence (and freezing rate) have a significant effect on the total water uptake and on the slow asymptotic water (Part 2) uptake, but not on the gradual water uptake (Part 1), or on the extract release volume or on the shear press forces. Freezing rates have a significant effect on the total water uptake, but not on the slow asymptotic water uptake (Part 2), on the gradual water uptake (Part 1), on the extract release volume or on the shear press forces. The highest total water uptake was found for the meat irradiated when fresh, and slow frozen at -2 2.2°C. The mechanism of the gradual absorption appears to follow a phenomena of water flow, as evidenced by the straight line relationship found in the plots of logarithm water uptake versus logarithm immersion time. / Land and Food Systems, Faculty of / Graduate