Elucidating the involvement of apoptosis in postmortem proteolysis in porcine muscles from two production cycles using metabolomics approach

Authors: MA, DANYI - Purdue University; SUH, DONG HO - Konkuk University; ZHANG, JAIYING - Purdue University; CHAO, YUFAN - Purdue University; DUTTLINGER, ALAN - Purdue University; Johnson, Jay; LEE, CHOONG HWAN - Konkuk University; KIM, YUAN H.B. - Purdue University

Submitted to: Scientific Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/27/2021
Publication Date: 2/10/2021
Citation: Ma, D., Suh, D., Zhang, J., Chao, Y., Duttlinger, A.W., Johnson, J.S., Lee, C., Kim, Y. 2021. Elucidating the involvement of apoptosis in postmortem proteolysis in porcine muscles from two production cycles using metabolomics approach. Scientific Reports. 11(1). https://doi.org/10.1038/s41598-021-82929-3.
DOI: https://doi.org/10.1038/s41598-021-82929-3

Interpretive Summary: Tenderness and water holding capacity greatly influence pork quality. However, environmental influences can impact these parameters leading to a poor eating experience for the consumer. Because postmortem protein breakdown plays an important role in affecting meat quality, it is important to characterize the relationships between the environment pigs are raised under and its influence on protein breakdown in the muscle. Therefore, the study objective was to evaluate apoptotic and proteolytic characteristics and metabolome changes of porcine muscles from two production replicates in which pigs were born in the summer and harvested in the winter or pigs were born in the spring and harvested in the summer. We hypothesized that metabolism features would be altered due to muscle type differences or environmental effects, which could have negative impacts on postmortem protein breakdown processes leading to meat quality variation. It was determined that seasonal production cycle effects on protein breakdown were present whereby pigs born in the summer and harvested in the winter had a decrease in biomarkers of protein breakdown. Data from this experiment have negative implications towards meat quality variation from pigs raised during different seasons.

Technical Abstract: Apoptosis has been proposed as upstream event of postmortem proteolysis, possibly affected by antemortal metabolic activities. To evaluate apoptotic and proteolytic attributes and metabolomic changes in postmortem porcine muscles, two repetitions of pigs (n=240) were raised in different seasonal cycles of consecutive years, July-Jan (weaned in July, 2016 and harvested in January, 2017) and Apr-Sep (weaned in April, 2017 and harvested in September 2017) in north-central Indiana. After slaughter, two muscles (longissimus dorsi and psoas major) from 10 carcasses were collected at 1d and 7d postmortem in each production cycle. Proteolytic characteristics of structural proteins, small heat shock proteins and apoptotic factors including desmin, troponin T, calpain 1, HSP27, aß-crystallin and cytochrome c were quantified using Western-blot assays. Mitochondria membrane permeability (MMP) was evaluated. Metabolome profiles of 1d samples were analyzed using the GC-TOF-MS platform. PM showed higher MMP than LD, but lower extent of calpain 1 autolysis (P < 0.05). Compared to July-Jan counterparts, Apr-Sep muscles showed concurrence of more extended apoptosis as indicated by higher MMP (P < 0.05), regardless of muscle effect. More extent of calpain 1 autolysis was observed in Apr-Sep (P < 0.05) regardless of muscle types. Troponin T degradation was higher in Apr-Sep, particularly in LD (P < 0.05). Small heat shock proteins were not affected by seasonal replicates. PM muscles showed increased HSP27 and aß-crystallin compared to LD (P < 0.05). Metabolomics profiling indicated muscle samples from Apr-Sep carcasses showed increased carbohydrates especially 6-carbon sugars, branched chain amino acids, and free fatty acids. In terms of seasonality, antioxidant amino acids histidine and aspartic acid and ascorbic acid were higher in July-Jan, suggesting higher antioxidant stress-defending activity (P < 0.05). Increased macronutrients in Apr-Sep could be related to higher cellular oxidative stress, favoring onset of apoptosis. As such, seasonal alternation of metabolism could render influential impact on meat quality development. The results of the present study provide initial evidence that extended apoptosis could promote proteolysis to a certain extent, while it is a muscle specific cross-talk. Early postmortem apoptosis might be facilitated by increased cellular macronutrient and oxidative stress, and inhibited by antioxidant compounds, subsequently impact proteolysis and meat quality development.