No abstract

Storage tests were conducted to identify and compare factors influencing the growth of Pseudomonas spp. as specific spoilage organism on fresh pork and poultry. Besides the extrinsic factor, temperature, the intrinsic factors, pH‐value, aw‐value, Warner‐Bratzler shear force (WBSF), d‐glucose, L‐lactic acid, fat and protein content were analyzed. The growth of Pseudomonas spp. was clearly dependent on temperature, with faster growth at higher temperatures. Furthermore, growth was faster on fresh poultry than on fresh pork resulting in shorter shelf lives at constant temperatures from 2 to 15C. Almost all of the investigated intrinsic factors were significantly different (P < 0.05) for fresh pork and poultry (except aw‐value and L‐lactic acid). Pseudomonas spp. counts correlated significantly to all investigated parameters in pork except WBSF and to four of the seven parameters in poultry (pH, aw, d‐glucose, L‐lactic acid). However, magnitudes of these correlations were low, which indicates minor influences on shelf life. Practical Applications Early spoilage of fresh meat can lead to food waste and thereby economic losses as well as the loss of consumer confidence. Until now, there have been no previous detailed studies describing and comparing different intrinsic and extrinsic parameters and their influence on the growth of Pseudomonas spp. as specific spoilage organism in different types of meat. Understanding the main impact factors on shelf life of fresh pork and poultry is a prerequisite for the development of methods and tools for improving processes in meat supply chains. In particular, the results can serve as a basis for the development of mathematical models that can predict the shelf life and remaining shelf life of both meat types.

Summary In this study, the influence of fluctuations of the cold chain on the growth of Pseudomonas spp. on fresh pork and poultry and, therefore, their shelf life was evaluated. Thus, four storage trials were examined. In each trial, shelf life at the control scenario (4 °C, constant) was compared with shelf life at two dynamic scenarios including temperature shifts from 4 to 7 and to 15 °C, respectively. Overall, fresh pork and fresh poultry showed similar spoilage patterns at dynamic temperature conditions with remarkable reductions in the shelf life when short temperature upshifts occurred at the beginning of the storage. Reductions were up to 2 days (up to over 30%), although the storage time with an abusive temperature was <5% of the total storage time. As expected, scenarios with shifts to 15 °C led to higher shelf life reductions than scenarios with shifts to 7 °C for both meat types.

The high growth rates of modern broiler breeds increased the risk for novel breast muscle myopathies as serious quality issue, relevant for the industry. In affected muscles, a depletion of the dipeptides carnosine and anserine was reported. Therefore, this study was performed to test whether a supplementation of the precursors histidine and β-alanine, alone or in combination can increase the dipeptide content in the breast muscle and improve meat quality. Ross 308 broiler chickens were supplemented with 3 different histidine:lysine ratios (0.44, 0.54, 0.64) of standardized ileal digestible amino acids ( SID ) combined with 0 or 0.5% β-alanine in total. The birds’ performance was recorded at different ages: birds were slaughtered in 2 batches after 33 and 53 d of life. Meat quality was tested at different time points after slaughter on breast fillets stored aerobically. The concentration of the dipeptides and amino acids in blood plasma and muscle tissue was tested postmortem at 35 and 54 d. All performance and meat quality data, as well as peptide and amino acid concentrations, of the 2 × 2 × 3 randomized block design were analyzed separately for the influence of both supplements and for slaughter age. Moreover, the influence of storage time was analyzed separately for meat quality parameters. At both slaughter ages, lesser feed intake ( P ≤ 0.005) and breast yield ( P ≤ 0.05) were observed in the birds receiving β-alanine. A greater SID histidine:lysine ratio increased the carnosine concentrations in blood plasma ( P < 0.001) and in skeletal muscle ( P < 0.001), whereas β-alanine increased carnosine in plasma at 35 d only ( P = 0.004). Anserine was increased in plasma and muscle of older birds ( P = 0.003), whereas carnosine was reduced in muscle tissue ( P < 0.001). The main impact on meat quality parameters was seen for the age of the birds and storage time of the fillets. In conclusion, the supplementation of histidine increased carnosine in breast muscle but both supplements showed only minor effects on meat quality.

A trial with different concentrations of DL-methionine (DLM) and DL-2-hydroxy-4-methylthiobutanoic acid (DL-HMTBA) in broiler feed was performed to investigate their effect on the meat quality parameters and the shelf life of breast fillet. In total, fillets from 210 male broiler chickens (Ross 308) were tested in seven groups with 30 animals each. Three different concentrations (0.04, 0.12, and 0.32%; on an equimolar basis) of either DLM or DL-HMTBA were added to a basal diet, summing up to seven treatment groups. After slaughter, fillets were packed aerobically and stored at 4°C. The investigated parameters comprised measurements of microbial as well as physicochemical parameters, such as pH, drip loss, cooking loss, and color measurements. Additionally, sensory investigations were conducted and shelf life was calculated. Mean pH values were between 6.1 and 6.4. Drip loss values were low, with mean values below 0.4%. The cooking loss ranged between 22% and 28% on average. The fillets showed a normal initial microbial quality (2.5 log10 cfu/g) and spoilage process with microbial counts of 8.5 log10 cfu/g at the end of storage. The study revealed a significant influence of methionine supplementation on the quality of broiler breast meat in comparison with the basal group. Methionine supplementation led to higher pH values and a higher water binding. Higher concentrations of methionine had a positive influence on the water-holding capacity by lowering the cooking loss. The L∗ value showed a significant negative correlation to the methionine concentration supplemented. No differences in physicochemical as well as sensory parameters could be detected between both methionine sources. The fillets showed a normal sensory spoilage process and a shelf life of 6 d. White striping was positively correlated to fillet weight as well as color values and significantly affected the Purchase Decision, the sensory investigation, and thus the shelf life of the samples.