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Enzymatic Browning

효소적갈변 ${효소가 관여하는 식품의 갈변. 식물식품 중에 다량으로 존재하는 페놀유는 폴리페놀 산화효소에 의하여 퀴논으로 되고, 이것은 중합하여 착색물질인 멜라닌을 만들어 낸다. 홍차발효는 이 반응을 이용하고 있다.}

NIR-Silage-nutritive value

PPO in red clover

M. Fothergill, M.E. Rees, F. R. Minchin and A.L. Winters

Institute of Grassland and Environmental Research

Plas Gogerddan, Aberystwyth

Ceredigion SY23 5EY. UK



Enzymatic browning is an important colour reaction and affects the appearance, flavour, texture and nutritional value of fruits, vegetables, herbage and even seafood. Polyphenol oxidase (PPO) is probably present in all plants and, in the presence of oxygen, catalyses the oxidation of phenolic compounds to form corresponding quinone intermediates. Once formed, these quinones undergo polymerization reactions leading to the production of melanins, which are known to exhibit both antibacterial and antifungal activity.

It is known that red clover, in contrast to most pasture legumes, has high levels of PPO (Jones et. al., 1995)). The quinones formed in red clover are highly reactive compounds and produce protein-quinone complexes in a similar manner to tannins. It is thought that it is this high level of PPO activity that confers protection of protein during the ensilage of red clover. The rapid formation of relatively stable protein complexes suggests that this phenomenon may also be relevant in a grazing context. Consequently, it has been hypothesised that high levels of PPO activity may be beneficial to improved animal live weight gain and reduced impact on the environment (Winters and Minchin, 2001).

Little information exists on whether levels of PPO activity differ between red clover cultivars or across the growing season. An existing red clover experiment provided the opportunity to compare the PPO profile of 6 red clover cultivars from two different sowing techniques (Direct Drilling and Broadcast sowing) replicated three times. We compared the two sowing techniques as they have produced plants of very different structure (due to different plant density) and it is known that stress affects PPO activity.

Leaves were sampled in the field during 2004 and immediately frozen using ‘Dry-ice'. The samples were taken back to the Plant Chemistry labs at IGER Aberystwyth and prepared by grinding in liquid Nitrogen. The resulting plant extract was then assayed for Basal and Optimal PPO activity.

Cultivars differed significantly (P<0.001) in basal, optimal and % utilisation of polyphenol oxidase (Britta and G. Pawera have low levels of activity).

There were significantly higher (P<0.001) levels of PPO activity in the early season (basal and optimal levels were 73% and 52% higher in July than in August)

Early heading cultivars had a higher optimal activity than the late heading cultivars (P<0.001) but only in early summer.

There were also indications of a cultivar x sowing method interaction early in the season (P=0.066).

It remains to be seen if these differences have a real and measurable effect on proteolytic losses in red clover silage



References

Jones, B. A., Hatfield, R. D. and Muck, R. E. (1995) Screening legume forages for soluble phenols, polyphenol oxidase and extract browning. Journal of the Science of Food and Agriculture. 1995. 67: 1, 109-112.

Winters, A. and Minchin, F. (2001). Red clover and the future of pasture legumes a san alternative protein source for ruminants. In IGER Innovations , p. 30-33. IGER Aberystwyth.

Rodriguez-Saona, L.E., Pereira, C., and Wrolstad R.E. 1997. Modeling the role of sugars, ascorbic acid, chlorogenic acid and amino acids in the non-enzymatic browning of potato chips. J. Food Sci. 62:1001-1005.

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J Food Science

C.Y.Lee