Microbial and Mycotoxin Decontamination of Red Pepper (Capsicum annuum L.) using Selected Emerging Food Processing Technologies
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Date
2021-12
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Addis Ababa University
Abstract
Mycotoxins are natural secondary metabolites of fungi occurring in foods which can cause adverse health effects. Contamination of foods with microorganisms and mycotoxins can occur at various stages along the value chain, and spices are not exception. Red pepper (Capsicum annuum L.) is one of the major spices consumed globally, recognized for its distinctive aroma, color, pungency and nutritional value. It also significantly contributes to the national economy for high producing countries like Ethiopia. However, natural contamination and occurrence of fungi with subsequent production of aflatoxins (AFs), ochratoxin A (OTA) and other mycotoxins in red pepper have posed a serious concern in the food system. Though mycotoxin contamination of red pepper has been evidently studied and well documented, studies regarding efficient decontamination techniques are scant. Therefore, this study aimed to investigate the impact of selected emerging food processing technologies (electron beam (e-beam), pulsed light (PL) and high pressure processing (HPP)) on the decontamination of naturally occurring microorganisms and mycotoxins in red pepper. Initially, the physicochemical, functional, thermal, oxidative stability and rheological properties of red pepper powder and paste were characterized. The compositional analysis showed that the red pepper powder contained 14.50, 44.00 and 7.57 g/100 g of crude fat, crude fiber and ash, respectively. The concentration of total phenols (TP), carotenoids and antioxidants activity of the powder were 1.04 g GAE/100 g, 374 mg c/100 g and 38.61 μmol TE/g, respectively. Findings on functional properties revealed that the bulk and tapped density were 395.1 kg/m3 and 583.4 kg/m3, respectively, indicating higher compressibility of the powder. In contrast, Hausner ratio (1.48), Carr‘s index (32%) and angle of repose (45°) indicated poor flowability of the powder. Particle size distribution also indicated that the volume weighted mean values D[4,3] of the powder and paste were 262.20 and 201.46, respectively. Emulsifying, oil and water absorption capacities of the powder were 47.5%, (1.41 to 1.73) g/g and (0.86 to 2.29) g/g, respectively. Higher glass transition temperature was observed for the powder (62.54 °C) than the paste (45.64 °C). The induction period indicated that red pepper was more stable against oxidation in powder form (5.2 h) than in paste (3.2 h). Rheological analysis revealed that the paste exhibited shear-thinning behavior at 25 °C. As aforestated, red pepper is an important spice with vital nutritional composition and techno-functional properties, and with immense potential for industrial application and product development. However, in recent years, frequent contamination with fungi and mycotoxins posed health concerns and hampering the export market. Thus, investigations on efficient decontamination techniques are critical. The first evaluated treatment was e-beam with variable doses of up to 30 kGy. Significant (P<0.05) reduction of yeasts, molds and total plate counts (TPC) were observed upon e-beam treatment, dose-gradient wise. Treatment at 6 kGy significantly (P<0.05) reduced yeasts and molds by 3.0 and 4.4 log CFU/g, respectively. Similarly, TPC was reduced by 4.5 log CFU/g at 10 kGy. Inactivation of yeasts and molds followed first-order kinetics, while TPC exhibited non-linear model fitted to Gompertz function (R2 = 0.9912). E-beam treatment was not efficient for the degradation of AFs but indirectly controlled their production by inactivation of mycotoxigenic molds. In fact, at the maximum e-beam treatment of 30 kGy, OTA was reduced by 25% retaining >85% of TP, carotenoids and antioxidants activity. Importantly, ‗slight differences‘ with the treatments on total color difference (ΔE*) were observed. Overall, e-beam treatments up to 10 kGy were effective in decontaminating the natural microbiota with minimal adverse effects on the physicochemical qualities of red pepper powder. The other decontamination treatment investigated in this study was PL. Red pepper powder was exposed to PL treatments up to 61 pulses, with an overall fluence ranging from 1.0 to 9.1 J/cm2. The highest fluence applied (9.1 J/cm2, 61 pulses, 20 s) resulted in 2.7, 3.1 and 4.1 log CFU/g reduction of yeasts, molds and TPC from 4.6, 5.5 and 6.5 log CFU/g, respectively. At the same fluence level, aflatoxin B1(AFB1), total AFs and OTA were reduced by 67.2%, 50.9% and 36.9%, respectively. There was a proportional increase in temperature from the absorbed PL energy, reaching maximum of 59.8 °C. The inactivation of both microorganisms and mycotoxins followed first-order kinetics (R2>0.95). With the lowest fluence (1.0 J/cm2), carotenoids and antioxidants activity reduced significantly (P<0.05). However, at higher fluence of 6.9 and 9.1 J/cm2, TP concentration increased. For all investigated PL intensities, there was a significant (P<0.05) change in color values of L* and b*. However, there was ―slight differences‖ in the ΔE* compared with untreated sample. The other emerging technique evaluated for decontamination of microorganisms was HPP. Predictive models of HPP treatments were developed and holding time (30–600 s) and pressure (100–600 MPa) were optimized. Treatment at 527 MPa for 517 s reduced TPC by 4.5 log CFU/g. Yeasts and molds counts were reduced to 1 log CFU/g at 600 MPa for 315 s. Within the treatment range, TP, carotenoids and antioxidants activity were 0.28 to 0.33 g GAE/100 g, 96.0 to 98.4 mg c/100 g and 8.70 to 8.95 μmol TE/g, respectively. Slight increase in these attributes by 2.5–6.7% was observed with increasing holding time and pressure. The ΔE* values up on treatments ranged from 0.2 to 2.8, which was within the category of ‗imperceptible‘ to ‗noticeable‘. Experimental results were fitted satisfactorily into quadratic model and higher R² values (0.8619–0.9863) and non-significant lacks-of-fit (p-value > 0.05) proved good prediction of the model. The optimum treatment of red pepper paste was at 536 MPa for 125 s for maximum desirability (0.622). Validation experiments confirmed comparable percentage of relative errors (0.7 to 16.7%) among predicted and experimental values. With the approaches of the present study, e-beam, PL and HPP could be used as alternative technologies for the decontamination of naturally occurring microorganisms and mycotoxins in red pepper with minimal changes in quality attributes.
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Keywords
Red pepper, Electron beam irradiation, Pulsed light, High pressure processing, Aflatoxin B1, Ochratoxin A, Kinetic modeling, Optimization