Yukiharu Nagata

Physico-chemical and processing quality of porcine M. longissimus dorsi frozen at different temperatures

Longissimus dorsi muscle from six pigs (24 h post-mortem) was cut into portions of similar size and shape (c. 700 g) and vacuum-packed in polyfilm. The muscle specimens were divided into three samples, one frozen at -20°C, another at -80°C and the third served as the control (not frozen). The meat sample frozen at -80°C was transferred to the -20°C freezer. After one month, both frozen pork samples were thawed at -2°C and drip loss (%) was measured. Hunter colour, metmyoglobin (MetMb) formation (%), water-holding capacity (WHC), TBA value, transmission value (TM) and myofibril fragmentation were also determined. There was no significant difference in drip loss for the two frozen samples. No MetMb formation could be detected and Hunter values were basically the same for all three samples. WHC, TBA value and TM were essentially the same for all three samples. TBA value was quite low for each frozen sample, indicating that lipid oxidation did not occur during freezing. Histological examination of both frozen samples indicated inter- and intracellular ice crystal formation at -20°C, and intracellular ice at -80°C, the extent being less than at -20°C. At -20°C, ice crystals were larger and muscle fibre diameter smaller than for the control or -80°C sample. Myofibril fragmentation in both frozen samples was significantly higher than in the control. Pork sausage was prepared from all three samples by adding 2% NaCl and 100 ppm NaNO(2). Cooking loss and colour forming ratios were essentially the same. The sausage sample made from the -20°C frozen meat was harder than that of the other two samples according to rheological measurement.

Anti-microbial Action against Verotoxigenic Escherichia coli O157:H7 of Nitric Oxide Derived from Sodium Nitrite

The levels of verotoxin-1 and verotoxin-2 released by verotoxigenic Escherichia coli O157:H7 treated in vitro with sodium nitrite, sodium chloride and several antibiotics were evaluated. Of the three strains of E. coli O157:H7 used in this study, two strains produced both verotoxin-1 and verotoxin-2, and one strain produced only verotoxin-2. Treatment of E. coli O157:H7 with sodium nitrite (6,000 mg/l, minimum inhibitory concentration) did not increase the levels of verotoxin-1 and verotoxin-2 compared with a treatment by sodium chloride or antibiotics. When the electron paramagnetic resonance spectrum of sodium nitrite-treated bacterial cells was examined at 77 K to clarify the mechanism for the anti-bacterial activity of nitric oxide derived from sodium nitrite, electron paramagnetic resonance signals with g-values of 2.035 and 2.010 were observed. These were identified as being derived from iron–nitric oxide complexes. It appears that the dinitrosyl iron complexes in the E. coli O157:H7 cells were generated from the reaction of iron-sulfur proteins (enzymes) with nitric oxide formed by the reduction of sodium nitrite. The amount of ATP was decreased by the presence of sodium nitrite in the cell suspension. These findings indicate that nitric oxide derived from sodium nitrite penetrated the cells and inactivated enzymes related to the respiratory chain.

Heme pigment content in meat as affected by the addition of curing agents

The effects of curing agents on the content of heme pigments (HP) in meat were examined. Minced porcine skeletal muscle was treated with NaCl, NaNO(2) and sodium ascorbate (NaAsA), separately or in combination, and stored at 2-3°C for 7 days. HP content decreased with increase in NaCl concentration and the decrease was about 50% and 80% at NaCl concentrations of 2% and 10%, respectively. Two percent NaCl prevented HP destruction, when previously mixed with 100 ppm NaNO(2) or 0·1% NaAsA. Although some decrease in HP content was noted following application of a mixture of NaCl, NaNO(2) and NaAsA, it was essentially the same as that of the control during 7 days of refrigerated storage. In a model solution containing the same curing agents as those applied to the meat. NaCl had no effect and myoglobin (Mb) content remained constant during storage. From the present results, endogenous muscle constituents appear to act in concert with NaCl to bring about a decrease in HP content.

Effects of ribose, xylose and arabinose on colour formation in processed meat products

The effects of ribose, xylose and arabinose on colour formation of meat products processed by emulsion curing were investigated in an aqueous model system under anaerobic conditions. Ribose markedly enhanced the colour forming ability, nitrite decomposition and reducing ability, depending upon its initial concentration; and xylose and arabinose exhibited some promoting effects on them. The colour promoting effects of ribose, xylose and arabinose increased with a rise in pH, in agreement with the results for reducing ability. This suggested that the reducing ability of ribose, xylose and arabinose plays a key role in promoting colour formation of meat products in emulsion curing.

Effect of Sarcoplasm from Porcine Skeletal Muscle on the Formation of Cooked Cured Meat Color

豚の内転筋より調製した筋漿を,水に対する透析法によって高分子と低分子の2画分に分け,亜硝酸塩の分解および発色効果に及ぼすこれらの画分の影響を比較検討した.高分子画分も低分子画分も共に亜硝酸塩を分解する作用ならびに発色を促進する効果が大きかったが,いずらの作用効果も低分子画分のほうが高分子画分より顕著であった.筋漿低分子画分をSephadex G-50によるゲル濾過法で分析した結果,管数35～42(Kd=0.8～1.1)内に顕著な発色促進効果を示す成分が溶出さら,得られた画分の発色促進効果と亜硝酸塩分解作用および還元力はよく対応し,またSH基,ニンヒドリン陽性物質および糖類を多く含むことが認められた.また紫外吸収特性による検討により,248nmにおける吸光度が最大を示す管数40(Kd=1.0)の画分中にかなりの量のイノシンあるいはその誘導体の存在が推定された.