Antioxidative effects of mango wastes on shelf life of pork products

Abstract

Peel and kernel often discarded during mango processing, are potential sources of antioxidants and could be utilised as additives to preserve meat products. The cultivar, physicochemical characteristics and stage of maturity are important factors that influence the antioxidant activity of mango flesh, peel and kernel. The cultivar Tommy Atkins, imported into New Zealand and the four cultivars; “Cat Hoa Loc”, “Cat Chu”, Ghep” and “Nam Dok Mai” grown in Vietnam were compared to determine which of the cultivars have antioxidant potential.

Tommy Atkins and Nam Dok Mai were less mature than the other three Vietnamese cultivars based on maturity score, firmness, total soluble solids (TSS), titratable acidity (TA) and Vitamin C. The antioxidant capacity of the mango flesh from all the cultivars ranged from 252.6 to 754.4 GAE 100g⁻¹ DW, (total phenolic content), 43.6 to 70.0 µmol TE g⁻¹ DW (ABTS radical scavenging activity) and 30 to 51.6 µmol TE g⁻¹ DW (DPPH radical scavenging activity). Mango peel antioxidant capacity was higher than flesh and ranged from 822.3 to 8084.9 GAE 100g⁻¹ DW (total phenolic content), 406.3 to 1188.3 µmol TE g⁻¹ DW (ABTS radical scavenging activity) and 210.6 to 735.4 µmol TE g⁻¹ DW (DPPH radical scavenging activity). The antioxidant capacity values of mango kernel was the highest and ranged from 6286.0 to 13888.8 GAE 100g⁻¹ DW (total phenolic content), 1066.3 to 2227.6 µmol TE g⁻¹ DW (ABTS radical scavenging activity) and 667.4 to 2205.7 µmol TE g⁻¹ DW (DPPH radical scavenging activity).

Flesh from Tommy Atkins and Cat Chu contained the highest antioxidant capacity than flesh from any other cultivar. Kernel from Tommy Atkins had the highest antioxidant capacity than any other cultivar whereas peel from Nam Dok Mai contained the highest antioxidant capacity than peel from any other cultivar. In all the cultivars investigated, kernel showed the highest content of total phenolic content and antioxidant capacities followed by peel then flesh, except for Nam Dok Mai whose kernel and peel contained similar antioxidant capacities.

The tannin content was significantly higher in kernel (21.3 - 54.7 g kg⁻¹ DW), than peel (7.9 - 22.9 g kg⁻¹ DW) than flesh (0.9 - 1.1 g kg⁻¹ DW) in all the cultivars. There were no oxalates detected in flesh in any of the cultivars. Small amounts of oxalates were detected in peel from all the cultivars and in kernel from Nam Dok Mai and Tommy Atkins. Peel and kernel from Cat Chu contained low levels of tannins and oxalates and are possible sources of antioxidants to prevent oxidative damage in food products.

Drying is usually used to produce dried products that can be mechanically incorporated into foods. Freeze, sun, vacuum and microwave drying reduced the hydrophilic antioxidants and antioxidant capacity of mango flesh whilst forced-air drying increased the total phenolic content (TPC) and ferric reducing antioxidant power (FRAP). In the case of peel, all the drying treatments reduced hydrophilic and lipophilic oxygen radical absorbance capacity (H-ORAC and L-ORAC) whilst microwave and freeze drying increased TPC and FRAP. For kernel, vacuum, followed by freeze drying increased the H-ORAC values and antioxidant capacity as measured by ABTS, DPPH and FRAP whilst the other drying treatments reduced the antioxidant activities.

The relationship between the physicochemical parameters (maturity) of Tommy Atkins mango fruits with the antioxidant capacity of their flesh, peel and kernel fractions as measured by their total phenolic content, ABTS, DPPH, FRAP, H-ORAC and L-ORAC activities was investigated. The physicochemical properties firmness, total soluble solids, titratable acidity, TSS:TA, vitamin C and moisture content were significantly correlated (p < 0.05) with the stage of maturity of the Tommy Atkins mango fruits. Thus, any one of the measured physicochemical parameters could be used as an indicator of fruit maturity in Tommy Atkins. All the antioxidant assays TPC, ABTS, DPPH, FRAP and H-ORAC were significantly correlated (p < 0.05) to each other indicating that phenolics in flesh, peel and kernel are good sources of antioxidants. In mango peel, only weak-to-moderate correlations were found between the lipophilic antioxidants (H-ORAC) and hydrophilic antioxidants (H-ORAC) or antioxidant capacity as measured by TPC, ABTD, DPPH and FRAP. Mango kernel from the less ripe mangoes with low maturity score, TSS, TSS:TA ratio and a high TA, firmness and vitamin C content were relatively high in antioxidant capacity relative to those from ripe mangoes. Peel colour was an unreliable index of the maturity of Tommy Atkins fruit or the antioxidant capacity of their peel, flesh and kernel.

The incorporation of freeze dried mango peel (1% w/w) or kernel (1% w/w) into pork sausages or patties on inhibiting lipid oxidation was investigated over a 10 day chilled storage period. There were small changes in TBARS (2-thiobarbituric acid reactive substances) and myoglobin over the first 4 days whilst off-odours and volatiles increased at day 4 in the control pork sausages and patties without any antioxidants. The volatiles, 1-pentanol (44.0%) and 3-hydroxyl-2-butanone (45.8%) in the sausages and hexanal (36.6%), pentanal (10.8%) and 1-pentanol (14.6%) in the patties were all identified as products of lipid oxidation and were generated by day 4. More volatiles, particularly hexanal, were released in the patties than in the sausages.

The addition of mango kernel (1% w/w) or peel (1% w/w) or synthetic antioxidant BHT (0.01% w/w) to the sausages and patties immediately changed TBARS (only observed in sausages), myoglobin and volatiles at day zero but there was no effect on colour or odour. The redness of sausages was reduced and the discoloration (hue) increased dramatically at day 2 and remained unchanged across the remainder of the storage period whilst the colour of the patties decreased gradually from day 0 to day 10. The addition of mango kernel, peel and BHT stabilised the colour of the sausages and patties especially the redness across the 10 day storage period. The antioxidative effects of the additives were more pronounced after day 4 when the addition of mango kernel or peel or BHT to the sausages and patties inhibited lipid oxidation as shown by the maintenance of stable TBARS, colour (a* and hue) and myoglobin and a reduction in off-odour and volatiles, compared to the controls. The addition of peel or BHT maintained the pleasant odour of pork sausages and patties for up to 4 days of storage and kernel for 6 days.

At 10 days, the mean TBARS values of the low (9.1% fat), medium (22.2%) and high (47.4%) fat control sausages were between 12.1 to 15.0 µmol MDA kg⁻¹ DW and sausages with added kernel between 3.1 to 3.8 µmol MDA kg⁻¹ DW. For patties, at 10 days, the TBARS values of control low, medium and high fat patties ranged from 12.3 to 29.2 µmol MDA kg⁻¹ DW and those with kernel from 6.9 to 7.9 µmol MDA kg⁻¹ DW. Mango kernel was more effective than peel or BHT in inhibiting lipid oxidation over the 10 day storage period. There was also an effect of the fat content (9.1 to 47.4% fat) of the product on the effectiveness of the added antioxidants to inhibit lipid oxidation. The TBARS in patties and the discoloration and loss in redness of the patties and sausages were higher in the high (47.4% fat) compared to low (9.1%) fat products. Furthermore, at 6 days for sausages and 4 days for patties the inhibitory effects on lipid oxidation was more effective with kernel than peel or BHT in the high and medium fat products.

Pork sausages with added kernel under O₂- permeable film at 4ºC were assessed to be microbiologically safe to consume over a 10 day storage period. Pork patties had a high TVC and were contaminated with E.coli and were assessed unsuitable for human consumption. The dried kernel and peel products themselves were judged microbiologically safe to use as food supplements. In addition, mango kernel exhibited antimicrobial effects against E.coli, staphylococci, coliforms, yeasts and moulds and TVC in the pork sausages.

Freeze dried mango kernel or peel contained antioxidants and if added to pork products extended their shelf life by inhibiting lipid oxidation (TBARS) and preventing changes in colour and odour. Kernel showed the highest antioxidant capacity, compared to peel or synthetic BHT. Dried mango kernel extended the shelf life of pork products for an additional 4 (patties) or 6 (sausages) days compared to patties or sausages without mango additives. In summary, dried mango kernel is an excellent natural source of antioxidants and prevents undesirable oxidative damage in pork products.