Abstract
Maple syrup, made by boiling the sap of Acer saccharum, is an important agriculture commodity in eastern Canada and New England. Although the collection season is relatively short, a rich progression in the sensory qualities of maple syrup can occur throughout the season. A risk associated with maple syrup production at the end of a season is the development of off-flavors that result in syrup with little to no commercial value. Maple syrup producers in Canada and the USA call this ‘buddy syrup’. In this study, sugar maple (Acer saccharum) sap was collected in sequential samples through the harvest season from stands across Ontario. Metabolomics analysis of the sap samples was performed by high-resolution mass spectrometry. This revealed an evolution of the chemical composition, mainly occurring 30 days prior to leaf emergence. The major chemical constituent of maple syrup, sucrose, decreased sharply in late season sap, driven by microbial activity. The alditol mannitol increased in late season sap to concentrations ≥2 mg/mL and is likely an indicator of the start of photosynthesis. Amino acids, notably methionine and asparagine were present in higher amounts in late season sap. Non-targeted analysis revealed a series of related compounds that contained quaternary ammonium moieties including choline, hercynine, trigonelline, glycine betaine and carnitine increased in late season sap. These classes of compounds could act as methyl donors during the heating/evaporation of sap into syrup, affecting taste. Based on descriptions of the nature of buddy syrup and an extensive literature on flavors in foods, the amino acids methionine and asparagine were found as likely precursors to the compounds responsible for buddy syrup.
Highlights
Maple syrup is made by boiling the sap of sugar maple (Acer saccharum) collected in the early spring when the temperature is above freezing during the day and colder at night
In 2019, maple sap samples were collected over the entire production season by 12 members of the Ontario Maple Syrup Producers Association (OMSPA)
In an effort to normalize the sap collection season across the regions, the Julian dates were transformed to a ‘days to bud break’ (DTBB) value using the model of Raulier and Bernier [22]
Summary
Maple syrup is made by boiling the sap of sugar maple (Acer saccharum) collected in the early spring when the temperature is above freezing during the day and colder at night. The Indigenous peoples where sugar maple grows have produced maple syrup/sugar for generations. Chemical analysis of sap samples from Acer saccharum ca/) with matching funds from MITACS (https:// www.mitacs.ca) OMSPA participated in the collection and organization of samples used in this study
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