I intend to evaluate the influence of the parameters inoculum ratio / must, fermentation time and temperature on the wine parameters, mainly ethanol. For this I need a same amount of sugars in the must to perform the experiments.
Could I do this by monitoring only soluble solids content (sucrose) in a refractometer, and occasionally adjusting with sugar, or would it be more convenient to monitor glucose, fructose and sucrose and try to fix values of these sugars for each sample?
can anybody help me?
Use HPLC equipped with an RI detector. Use a Waters (or equivalent) Sugarpak column and water as the mobile phase.
Pretreat the sample with a C18 Seppak (to eliminate dyes) and desalt with a Sephadex G15 media.
Thanks a million
But would know answer me what is more convenient to monitor? sucrose in geral or glucose and frutose?
Sucrose is a polymer of fructose and glucose. You will have to use the enzyme 'Invertase' to determine the decrease in the HPLC peak DP2 which is sucrose (it splits to form fructose and glucose). Maltose (from corn syrup) is also a DP2 peak but does not react with Invertase.
I will use grape must. In the grapes the sugars presents are glicose e frutose ok? Then wouldn´t be more better to monitor this two sugars in the HPLC?
The most important is to now the reduct sugar that you have in the grapes. This is the preferences to the micorganisms.
You can monitor that using Benedict or Fehling reactive.
O fato é que vejo muitos trabalhos monitorando o teor de açucares pelo grau Brix que é baseado no teor de açucares totais soluveis (sacarose). Esta prática está errada então?
Adriano,
Yes. You can also use a Biorad Aminex column too though the UV absorbs at 210 nm (along with everything else) unless you are using PAD, ESLD, MS...
Essa prática não está errada se você considerar que o teu microrganismo tem enzimas suficiente para quebrar todos os açúcares, por outro lado você teria condições de saber quanto de açúcares redutores (principalmente porque ele te fornece os monossacarídeos presentes) você tem no total de açúcares disponíveis. A preferência é sempre pela glicose.
Olá Adriano, não é errado usar o ºBrix, mas assim consegue ter o valor total aproximado dos açucares redutores no mosto. Na minha opiniao basta monitorizar a glicose e fructose, usando HPLC.
You need to do a lot more reading in terms of which sugars a preferentially fermented for as has already been mentioned sucrose is a disaccharide and will be fermented last because the yeast needs to excrete invertase in order to break the disaccharide into monosacharide unites of glucose and fructose. These can then be fermented. Also there is the need to understand the influence of the total sugar level for this affects the yeast's ability to ferment the must and hence the individual sugars. Refractometers are just too simplistic. Don't equate the refractometer reading with sugars for it is sensitive to the effect of all soluble solids on the refractive index as well as the alsohol as it is fermented. Fine for industrial use but for research go with the HPLC. Of course the level of sucrose in grape must is quite low anyway.
I think it will be better to monitor glucose, fructose and sucrose levels for each sample.
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