Zerihun, Efrem Mengistu (2015) Effect of Incandescent Display Light and Ethiopian Spices on the Quality of Raw Beef. PhD thesis, Addis Ababa University.
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Abstract
Meat purchasing decisions are influenced by color more than any other quality factor when selecting beef at retail, because consumers use color as an indicator of freshness and wholesomeness. Due to this, meat retailers usually keep the meat display area well lighted to attract consumers. In Ethiopia almost all butcher shops are displaying the beef carcasses under high power (400 watt) incandescent lamps through an open window of display booth. Displaying carcasses under this condition might have a potential to accelerate lipid oxidation and the formation of dark brown muscle color. Moreover, at these butcheries, many people frequently consume raw meat (kurt siga or kitfo) by using Ethiopian spices sauce prepared from the powders of chili pepper, African birds eye and mustard seeds. Therefore, this study focused on the evaluation of the effect of incandescent display light (at room temperature) and Ethiopian spices on the color and oxidation stability of raw beef. The beef samples which used in this study were bought from butcher shops (Addis Ababa, Ethiopia and Ghent, Belgium) from muscle of semitendinosus, longissimus dorsi and triceps brachii. The spices samples which are commonly consumed with raw beef were chili pepper (capsicum annuum), African birds eye (capsicum minimum) and mustard seed (brassica nigra), were purchased from Merkato market, Addis Ababa. The analyses undertaken in this research were color change of displayed raw beef slices (L*, a*, b*, Chroma, hue angle & ΔE, by colorimeter and image analysis), lipid oxidation (TBARS), myoglobin species content (oxymyoglobin and metmyoglobin), total aerobically count, temperature elevation, antioxidant activities (free radical scavenging/DPPH, reducing power, TEAC/ABTS), total phenol, total flavonoids and SPME-GC-MS to identify aromatic compounds of mustard seeds. The raw beef slices exposed under incandescent light continuously at 6280±210 lux showed higher TBARS value, ΔE, hue angle & MMb%, and lower L*, a*, b*, Chroma & OMb% value than the raw beef slices kept in the dark at room temperature as the light exposure time increased. These results are a clear evidence of the influence of high power incandescent display light and the light exposure time on color and oxidation stability of raw beef. Moreover, the covered raw beef samples have more color stability than the opened displayed raw beef samples. However, the covered raw beef samples exposed to incandescent light exhibited significantly lower oxidation stability and higher temperature on meat surface compared to open displayed raw beef samples. One of the interesting result was that the yellowness (b*) value of raw beef sample exhibited greater value than the redness (a*) value of covered displayed beef samples compared to opened displayed beef samples. At starting time (0hr) a* value was significantly higher (p<0.05) than b* value but after display, the covered sample acquired higher b* value than a* value in all the displayed periods. This study also revealed that the color stability of displayed raw beef was highly related to the muscle type. Among the selected three beef muscle types the semitendinosus showed better color stability than the longissimus dorsi and triceps brachii muscle types and the triceps brachii exhibited the lowest color stability. The specific wavelengths of the light spectrum upon meat color stability were evaluated by filtered out short wavelength 450 nm (blue), medium wavelengths (green & yellow) and long wavelength 650 nm (red). The display light from the shorter wavelengths (450 nm) exhibited a higher discoloration on raw beef. However, the display light from the long wavelength (red, 650 nm) was reduced the discoloration of displayed raw meat. The ΔL*, Δa* and ΔE* values of short wavelength of visible light (blue spectra at 450 nm) was significantly higher (p < 0.05) than long wavelength (red, 650 nm). In addition, the rate of decrease of the color parameter L*, a*, b* and chroma values was higher in transparent (4.99±0.06 lux) and yellow filters (4.50±0.06 lux), which have higher illuminance than others. It was also observed that the selected spices extracts were found to exhibit effective lipid antioxidant activity of raw beef samples which were stored in a dark refrigerator for two weeks. All these spices extract enhanced color stability in raw beef especially until one week of storage period in a dark refrigerator. In addition, all spices extract performed well in preventing the growth of aerobic bacteria on the surface of spices treated raw beef samples during two weeks storage period and they were able to maintain fresh color as compared to the controls which were not treated by the spices. However, the dosage of spices extracts had no significant difference on color and oxidation stability of raw beef samples. The spices analyzed were rich in total phenol and flavonoids with high antioxidant activities. Mustard seed, African bird‘s eye and chili pepper showed IC50 value of 85 μg/ml, 172 μg/ml and 186 μg/ml respectively, in DPPH method. The TEAC value of chili pepper, African bird‘s eye and mustard seed were 5.75±0.07, 5.75±0.04 and 5.22±0.09 mgTE/g, respectively. The reducing power of the spices extracts increased with increasing concentration and these extracts exhibited the following order: mustard seed > pepper > African bird‘s eye. Total phenolic and total flavonoid contents of spices extracts showed the following order: chili chili pepper > African bird‘s eye > mustard seed. The chili pepper (capsicum annuum) exhibited the highest total phenolic and total flavonoid contents, 16.81±0.25 mg galic acid equivalent per gram of dry weight and 8.74±0.91 mg catichin equivalent per gram of dry weight respectively. The mustard seed extracts were lowest comparing to the two spices, 10.03±0.52 mg galic acid equivalent per gram of dry weight and 0.36±0.26 mg catichin equivalent per gram of dry weight respectively. The germinated mustard seeds exhibited more antioxidant activity, and total phenol and flavonoids contents than the raw/dry mustard seeds and showed a consistent trend, where 3 days germinated > 1day germinated > raw mustard seeds. In the analysis of aroma compounds of mustard seeds, several sulfur contained compounds were identified by SPME-GC-MS. Within the sulfur contained compounds, the ally isothiocyanate was the most dominant. In conclusion, high power incandescent display light decreased meat color quality faster than meat samples stored in the dark. In addition, the display light from the shorter wavelengths exhibited a higher discoloration on raw beef samples than the long wavelength. Hence, the use of display light sources with a reduced radiation in the short wavelength range is necessary to reduce the deterioration in quality of displayed meat. Generally, use of high intensity lighting for meat display may result in more and faster meat sales, but if sales do not keep pace with discoloration of meat, loss of profit may result. Moreover, the Ethiopian spices are rich in phenolic compound and demonstrated good antioxidant activity. Hence, people eating them with raw beef may benefit as they can to protect themselves against oxidative damage. These spices can be used as a source of antioxidant for production of shelf stable food products and also as a source of healthy compounds for the development of dietary supplements via advanced research and development activities.
| Item Type: | Thesis (PhD) |
|---|---|
| Subjects: | H Social Sciences > H Social Sciences (General) Q Science > Q Science (General) Q Science > QH Natural history > QH301 Biology Q Science > QL Zoology |
| Depositing User: | Selom Ghislain |
| Date Deposited: | 27 Jun 2018 14:19 |
| Last Modified: | 27 Jun 2018 14:19 |
| URI: | http://thesisbank.jhia.ac.ke/id/eprint/6051 |
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