A meta-analysis investigating the influence of citrus by-product pretreatment on lipid oxidation levels in stored chicken meat

This study extensively investigates the impact of citrus by-products on the oxidative stability of chicken meat. The literature review, spanning from 2000 to 2023, involved a thorough screening process, adhering to stringent selection criteria guided by PRISMA-P guidelines. The utilization of Hedge’s model meta-analysis to examine the distinctions between the control and treatment groups, wherein the random effect accounts for inter-study differences, and the fixed effect pertains to the impact of the addition of citrus by-product to chicken meat. Citrus by-products from various fruits, applied under diverse conditions, consistently and significantly reduced TBARS levels throughout the storage period, resulting in an overall mean effect size of -2.57 (P<0.001). While most citrus types displayed a non-significant trend with prolonged storage, both seed and peel components exhibited a significant reduction in TBARS levels (P<0.05). Notably, citrus by-products, especially in whole chicken meat and through marination pretreatment, demonstrated substantial reductions in TBARS values (P<0.01). This metaanalysis underscores the potential of citrus by-product to effectively enhance the oxidative stability of chicken meat during storage, providing valuable insights for further research and practical applications in food preservation.


Introduction
The heightened concentration of essential nutrients in animal products has led to a substantial 60% increase in global meat consumption over the last 25 years [1].Poultry meat, particularly favored in lower-middle-income countries, has become the most extensively consumed type due to its relatively lower cost, considerable nutritional value, and ease of processing [2].Consequently, there has been a proliferation of innovations, particularly in the preservation of chicken meat, seen as a critical necessity for ensuring food safety in the worldwide meat trade [3].Moreover, substantial amounts of industrial and household waste, notably from various food sources like citrus fruits, often remain underutilized.From this perspective, there is a pressing demand for inventive processing of citrus waste, involving peels, seeds, and another biomass.Reports suggest that these citrus waste components still contain active food-preserving agents, which are valuable for both conservation and processing.Furthermore, the acknowledged elevated antioxidant efficacy of citrus peel extract provides a beneficial means to prolong the freshness of poultry meat.
The high nutrient content, particularly water, fat, and protein, in chicken meat has been identified as the primary factor leading to the degradation of meat quality [4].The major contributors to the deterioration and reduction in poultry meat products flavour, colour, texture, and nutritional value are lipid oxidation and rancidity effects [5].The oxidation reactions between the fatty chains of chicken meat and exposure to oxygen cause this rancidity.The unpleasant taste results from the decomposition of lipids, forming peroxide and aldehyde compounds, which are identified through the measurement of thiobarbituric acid reactive substances (TBARS) [6,7].
In order to prevent the occurrence of rancidity in chicken meat products, measures are taken during the preparation process to include antioxidants.Techniques such as coating, marination, and curing are applied to treat chicken meat, with a focus on improving sensory quality and prolonging shelf life, particularly through the curing method [8,9].This pretreatment approach involves the use of plantderived ingredients rich in substances like antioxidants, phenols, and flavonoids [10][11][12].Antioxidants play a crucial role in preventing the auto-oxidation of meat fat by donating hydrogen groups, thereby inhibiting the formation of initial free radical agents and impeding the oxidation process [13].In recent years, natural antioxidants, such as citrus extract, which has high antioxidant and antibacterial properties, have been compared to synthetic antioxidants.Citrus (Citrus L.) contains important phytochemicals (catalase, terpenoids, flavonoids, organic acids, etc.) as antioxidant and antibacterial agents that can be utilized as a rancidity preventer in meat products [14].This phytochemical ingredient is also present in many parts of citrus fruits; hence, it is commonly used as a by-product of citrus fruits to harness its antioxidant and antibacterial properties [15].Therefore, the utilization of citrus byproducts has potential benefits for use as an anti-rancidity agent in chicken meat products, which are important for development.An insightful explanation of this topic is needed.Based on the aforementioned facts, this study intends to provide additional comprehensive data on the effectiveness of using citrus fruits and their by-products as natural preservation agents for chicken meat products by looking at TBARS values using the meta-analysis approach.

Search, selection, extraction, and validation of data
The exploration of the effects of citrus by-product on the oxidative stability of chicken meat, assessed through TBARS, involved the use of keywords such as "citrus peel", "citrus seed", "citrus peel and seed", "chicken meat", and "TBARS" during the literature review.A thorough investigation was carried out through the Google Scholar, Science Direct, and Scopus search engines.The search period spanned from the year 2000 to 2023, resulting in a total of 11,221 sources.By employing the filtering tool in the search engine application, we conducted filtering to exclude types of writing such as reviews, critiques, opinions, and conference papers.As a result, a subset of around 2,500 articles was retrieved from the search.From this pool, the titles were further screened based on specific criteria: the research must be experimental, should incorporate TBARS as a parameter, and the subject of the study must involve broiler chicken meat.Consequently, 103 articles were identified as relevant.
In order to guarantee the quality and compliance with reporting standards, the subsequent procedure entailed verifying the chosen articles through the utilization of the preferred reporting items for systematic review and meta-analysis protocols, commonly recognized as PRISMA-P [16].This additional validation process resulted in the final selection of approximately 10 articles that meet the criteria and are considered suitable for inclusion as secondary data sources in the upcoming metaanalysis.This rigorous selection process ensures that the chosen articles align with the research objectives and maintain a high standard of experimental design, contributing to the robustness and reliability of the subsequent meta-analysis.Note: Add.= the incorporation of citrus by-product concentration into chicken meat (% relative to the total weight of the meat), N.D. = no data, Ref. = reference.
This study involves utilizing extracts derived from different citrus fruits, including Citrus spp., Citrus hystrix, Citrus limon, Citrus paradisi, Citrus sinensis, and Citrus unshiu, under diverse conditions applied to chicken meat.All citrus employed are extracted in the form of extracts using food-grade organic solvents.The extraction process is conducted from various sections of the chicken meat, encompassing the whole, breast meat, drumette, and wing.Additionally, the utilized by-products include seed and peel.Subsequently, the chicken meat undergoes different pretreatments such as marination, coating, or curing, with storage temperatures ranging from 4 to 20 degrees Celsius and varying storage durations, spanning from a few days to several months.The findings of these investigations can be located in citations [17] to [26] (Table 1).

Calculation of effect size
The definition of control involves a treatment without the administration of citrus, while the treatment group entails the introduction of citrus into broiler chicken meat.This meta-analysis employs the Hedges method in calculating the effect size [27], and the cumulative effect size or mean deviation (SMD) is computed as follows: where   signifies the reciprocal of the variance in sampling:   = 1   ⁄ .The precision of the effect size is presented as a 95% confidence interval (C.I.) [28,29].All these meta-analyses were conducted using OpenMEE 2.0.

Result and discussion
The meta-analysis of TBARS values in chicken meat treated with citrus by-product reveals a substantial impact on oxidative stability throughout the storage period, spanning from 0 to 10 days.At the initiation of storage (0 days), the effect size (SMD) was -0.48, indicating a slight reduction in TBARS, though not statistically significant (P=0.091).However, as the storage duration progressed, the antioxidative effect became increasingly pronounced.After 2 days, a significant decrease in TBARS levels was observed (SMD = -1.03,P<0.001), and this trend continued with escalating potency over subsequent days.The effect sizes became progressively more negative, reaching -5.66 at 10 days of storage (P<0.001).The individual day analyses also reflect a significant reduction in TBARS levels at each time point: 4 days (SMD = -1.12,P<0.001), 6 days (SMD = -2.29,P<0.001), 8 days (SMD = -3.84,P<0.001), and 10 days (SMD = -5.66,P<0.001).The overall mean effect size across all time points was -2.57(P<0.001),highlighting a substantial and consistent reduction in oxidative damage due to citrus by-product pretreatment.Nevertheless, nearly all conditions of long-term storage at a temperature of 4°C exhibit a more pronounced decrease in TBARS (P<0.05).The high heterogeneity observed across all time points (I² > 80%) underscores the reliability of these findings.Most types of citruses do not show significance (P>0.05) with increasing storage time for chicken meat, although there is an observed trend indicating a decrease in TBARS values for all citrus types (figure 1a).The seed and peel components of citrus significantly (P<0.05)reduced TBARS during the storage of chicken meat (figure 1b).Extracts from citrus fruits significantly reduce TBARS values (P<0.01;figure 1c).The whole chicken meat part shows responsiveness to citrus treatment, with a significant decrease in TBARS values (P<0.01;figure 1d).Similarly, pretreatment through marination significantly (P<0.01)reduces TBARS during the storage process (figure 1e).Examining other research that investigates the influence of antioxidants on TBARS levels in meat storage can offer a broader perspective on these findings.For example, multiple studies have noted a comparable antioxidative impact when using different antioxidant compounds in chicken meat.These studies reported a significant reduction in lipid oxidation in chicken meat treated with herbs and their by-products over a 10-day storage period [17,18,30,31].This outcome corresponds with the substantial decrease observed in the present meta-analysis, reinforcing the idea that the use of citrus by-products is similarly effective to other antioxidant interventions in alleviating oxidative damage in meat.The antioxidants in citrus are believed to come from various compounds present in the fruit.Citrus fruits contain a diverse range of antioxidant elements, including ascorbic acid (vitamin C), essential oil, flavonoids like hesperidin and naringin, carotenoids such as beta-carotene, phenolic acids, and antioxidant minerals like selenium and manganese [14,[32][33][34][35].For instance, the potential of citrus essential oil to reduce oxidants is attributed to its antioxidant properties, specifically from compounds like limonene and linalool [12].These components play a protective role for the body cells against free radical damage and contribute to the reduction of inflammation.Additionally, citrus oil may boost the activity of antioxidant enzymes like superoxide dismutase [36].

Summary
In summary, extracts from citrus by-products can mitigate lipid oxidation in chicken meat during storage process.Specifically, the peel and seed by-products derived from citrus prove effective in minimizing lipid oxidation in chicken meat.

Figure 1 .
Figure 1.The regression is centered on evaluating the effect size derived from changes in TBARS values in chicken meat following the addition of citrus by-product.The observed conditions include differences in a. citrus types, b. extraction techniques, c. sections of chicken meat, and d. applications of pretreatment.

Table 1 .
Selected literature for the compilation of meta-analysis data.

Table 2 .
Alterations in TBARS levels over the storage duration in chicken meat subjected to pretreatment with citrus.
a Thiobarbituric acid reactive substances b Observed data analyzed in meta study c Sum means different d Standard error e I 2 in meta-analysis gauges heterogeneity among study effect sizes