Formation of volatile organic compounds during the fermentation of maize as affected by sealing time and silage additive use

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Abstract
The study investigated the production of volatile organic compounds during the fermentation of maize containing 26.8% dry matter (DM). Forage was ensiled without additive or treated with 2 ml/kg of a chemical silage additive (SA) containing per litre 257 g sodium benzoate, 134 g potassium sorbate and 57 g ammonium propionate, and either sealed immediately or with a delay of 24 h. During the fermentation process, DM-losses, fermentation pattern (including ethyl lactate [EL] and ethyl acetate [EA]) and yeast numbers were determined. Delayed sealing and no SA resulted in highest DM losses with significant interactions between sealing time (ST) and SA on all sampling days (p < 0.001). The effects on organic acid production were variable depending on storage length. Ethanol production was affected by ST and SA, but promptly sealed silage treated with SA had consistently the lowest concentrations. Higher ethanol content during fermentation was associated with higher DM losses, as reflected by a strongly linear, positive relationship (R2 = 0.70, p < 0.001). Compared with promptly sealed silage, the counts of yeasts were higher after delayed sealing during the first 7 d of storage (p < 0.001). Moreover, SA reduced yeast numbers compared with untreated silage (p < 0.01). EL concentrations increased throughout storage, whereas EA acetate accumulation was very rapid and intense already during the early stages of fermentation and peaked on d 34. The differences in concentrations and accumulation pattern between EL and EA, especially during the early fermentation phases, make evident that their synthesis was facilitated by different pathways and reactions, respectively.

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