Egyptian goose (Alopochen aegyptiacus) : sensory, biochemical and physical meat quality as affected by gender, diet and ageing

Geldenhuys, Greta (2014-12)

Thesis (PhD(Food Sc))--Stellenbosch University, 2014.

Thesis

ENGLISH ABSTRACT: In Southern Africa, the hunting of wildfowl species has increased considerably in the past few years. Crop farmers incur major financial losses due to the feeding activities of Egyptian geese (Alopochen aegyptiacus); consequently a large number of geese are hunted in an attempt to reduce the damage caused. With the current absence of scientific information baseline research investigating the meat quality of this species is essential. The sensory profile of Egyptian goose meat was found to be very distinct in relation to the characteristics of other well-known fowl species. It has very strong game aroma and flavour attributes with a prominent metallic aftertaste. The intense aroma and flavour notes were linked to the substantially higher iron content, as well as the high overall polyunsaturated fatty acid content as revealed by chemical profiling. The trained sensory panel also found the meat to be very tough (high shear force) compared to the other species. To identify the factors which may affect the overall consistency of the meat quality, the influence of three main effects namely; season (grain vs. non-grain diet), gender and portion was investigated. This revealed that season had the largest effect and harvesting periods should therefore be considered. The main issue is the higher intramuscular fat (IMF) content in winter (July), as well as the substantial difference in the fatty acid profiles of the two seasons. The forage vs. grain based diets during certain periods of the year leads to variation in the content of key fatty acids in the meat i.e. oleic acid, linoleic acid and α-linolenic acid. In winter, the meat had a characteristic, prominent game and metallic aroma while the summer (November) profile was governed by “sweet-oily-duck” and beef-like sensory notes. The fatty acid differences also result in variation between the omega 6 to omega 3 ratios of the seasons; the portions from winter are within the recommendations (ratio<5) and those from summer not. Regarding gender, the females had a lower carcass yield but higher IMF content. The female breast portion was also more tender (lower shear force). In attempting to elucidate the toughness of the meat, possible causes have been proposed. The pH decline in the pectoralis muscle occurs quite rapidly and it is possible that the high rigor temperature (>20 °C) may contribute to the increased toughness. Regardless of the proteolytic enzyme activity during the rigor period, the meat is still tough at 36 h post mortem and the proteolytic contribution may be overshadowed by the background toughness, i.e. the connective tissue content and fibre structure. The latter was confirmed when the breast portions were aged for 14 days and no change (decline) in the shear force values was observed even though myofibrillar degradation did occur (during ageing). Given the lack of a decline in the shear force, the aging of Egyptian goose meat as a means of improving the overall toughness cannot be proposed without further research. The study in its entirety provides substantial proof that the commercial utilisation of Egyptian goose meat is feasible.

AFRIKAANSE OPSOMMING: Die jag van wildsvoël spesies in Suider-Afrika het aansienlik toegeneem in die laaste paar jaar. Graanboere lei jaarliks groot finansiële verliese as gevolg van die voedingsgedrag van kolganse (Alopochen aegyptiacus). Gevolglik word ‘n groot hoeveelheid ganse elke jaar geoes om sodoende die skade te verminder. Met die huidige tekort aan wetenskaplike inligting is grondslag navorsing rakende die vleiskwaliteit van hierdie wildsvoël spesie noodsaaklik. Die sensoriese profiel van kolgansvleis is baie uniek in vergelyking met die vleis van ander bekende voël spesies. Dit word gekenmerk deur die sterk wildagtige aroma en geur tesame met ‘n baie prominente metaal nasmaak. Hierdie intense aroma en geur hou verband met ‘n baie hoër yster-inhoud, asook ‘n hoë poli-onversadigde vetsuur profiel soos uitgewys deur die chemiese karakteriserings studie. Die opgeleide sensoriese proepaneel het ook die vleis van hierdie voël spesie beskou as baie taai in vergelyking met die vleis van ander spesies. Ten einde te bepaal watter faktore die algehele variasie in vleiskwaliteit sal beïnvloed, is drie hoofeffekte naamlik, seisoen (graan teenoor nie-graan dieet), geslag en porsie ondersoek. Die verskeie studies het uitgewys dat seisoen die grootste invloed het en daarom sal die periodes waarin ganse geoes word in ag geneem moet word. Die hoër intramuskulêre vetinhoud in winter (Julie), asook die aansienlike verskil in die vetsuur profiele van die twee seisoene is die vernaamste verskille. Die weiding (hoofsaaklik gras) teenoor graan diëte wat gevolg word in sekere dele van die jaar lei tot variasie in die inhoud van belangrike vetsure (oliensuur, linoleïensuur en α-linoleensuur) in die vleis. In die winter het die vleis die kenmerkende en prominente wild geur en metaalagtige nasmaak getoon terwyl die profiel in die somer (November) hoofsaaklik bestaan het uit “soet-olierige-eend” en beesvleis geure. Die vetsuur verskille lei ook tot ‘n verskil in die omega-6 tot omega-3 verhouding van die seisoene; in die winter is die porsies binne die aanbevole voedingsvereistes (<5) terwyl die somer porsies nie aan hierdie vereistes voldoen het nie. Rakende die invloed van geslag, het die vroulike voëls ‘n laer karkas massa getoon tesame met ‘n laer intramuskulêre vetinhoud. Die borsie van die vroulike kolganse was ook sagter. In ‘n poging om die taaiheid van kolgansvleis te verklaar, is ‘n paar moontlike oorsake voorgestel. Die na-doodse pH daling in die borsspier vind redelik snel plaas, daarbenewens is dit ook moontlik dat die hoë temperature (>20 °C) waartydens rigor mortis plaasvind, kan bydrae tot die taaiheid. Ongeag die werking van die proteolitiese ensieme tydens die rigor periode was die vleis steeds taai 36 uur na dood, daarom was die proteolitiese bydrae moontlik oorskadu deur die agtergrond-taaiheid, dit wil sê die bindweefsel inhoud en vesel struktuur. Laasgenoemde is bevestig toe die borsspiere verouder is vir ‘n tydperk van 14 dae. Geen verandering (afname) in die instrumentele taaiheid is waargeneem nie, selfs al het miofibrillêre afbraak plaasgevind. Aangesien daar geen afname in instrumentele taaiheid opgemerk is nie kan veroudering van kolgansvleis, met die doel om die taaiheid te verbeter, nie aanbeveel word voor verdere navorsing nie. In geheel voorsien hierdie studie beduidende motivering rakende die moontlike kommersiële aanwending van kolgansvleis.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/95871
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