Potential of fluorescence spectroscopy for the characterisation of maple syrup flavours.

BACKGROUND: Maple syrup has high maket value. It is produced in North East America from the heat-evaporated sap of Acer saccharum Marshall. For marketing purposes, there is interest in defining its flavour profile in a consistent and repeatable manner. An experiment was undertaken to explore the potential of autofluorescence of maple syrup induced at 275 and 360 nm to characterise flavours. RESULTS: A mixed data factor analysis revealed two independent groups of variables. One represents early season woody and late season empyreumatic flavours. The other is related to off-flavour, confectionery and maple flavours. Maple and confectionery flavours are subtle, difficult to distinguish and opposed to off-flavour. There were clear relationships among the two groups and fluorescence profiles. For each of the five basic flavours, discriminant models based on partial least squares regressions were developed. For each sample of syrup, flavours combined to form flavour profiles, and the results from the five discriminant models were aggregated to reproduce these profiles. For excitation at 275 nm, the woody/off-flavour and confectionery/empyreumatic/maple flavour profiles were classified correctly 86 and 78% of the time (cross-validation) respectively. CONCLUSION: Induced autofluorescence spectra were shown to contain information related to maple syrup flavours. This fluorescence-flavour relationship is not considered quantitative yet, and further research avenues are proposed.

Determination of naturally occurring formaldehyde levels in sap and wood tissue of maple trees using gas chromatgraphy/mass spectrometry.

The occurrence of formaldehyde in sap and wood tissue of treated and untreated maple sugar trees was investigated using GC/MS. Samples were collected at different periods of the 2009 season and at different locations in Quebec, Canada. The natural concentration of formaldehyde found in untreated samples varied according to periods and locations and ranged from below the LOQ to 1.82 mg/kg for sap samples and from 2.39 to 8.92 mg/kg of fresh tissue for wood samples. Late season samples tended to have higher concentrations of formaldehyde. Samples of sap and wood tissue from tapholes treated with solutions of formaldehyde showed increased concentrations of formaldehyde for many days after treatment and were clearly distinct from untreated samples. These results will be useful to elaborate new inspection procedures for sugarbushes to control the illegal use of formaldehyde.

Biotransformation of sucrose rich Maple syrups into fructooligosaccharides, oligolevans and levans using levansucrase biocatalyst: Bioprocess optimization and prebiotic activity assessment.

Maple syrup was investigated as a source to produce FOSs and ß-(2-6)-linked-oligolevans/levans. The modulation of this biotransformation was achieved through the control of Maple syrup °Bx and reaction conditions. Reaction time was identified as the most influential factor for the oligolevans/FOSs production in Maple syrup 30°Bx reaction system as well as for the oligolevans/levans synthesis in the 66°Bx one. In the predictive model of oligolevans/levans production in Maple syrup 60°Bx, the interactive effect between levansucrase unit and reaction time was significant (p-value of 0.0008). The optimal conditions for oligolevans/FOSs production (109.20 g/L) in Maple syrup 30°Bx were 3.73 U/mL, pH 6.60 and 23.12 h; while 5 U/mL, pH 6.04 and 29.92 h were identified as the optimal conditions for oligolevans/levans production (147.09 g/L) in Maple syrup 66°Bx. As compared to inulin-type commercial FOSs, the fermentation of oligolevans/FOSs from Maple syrup led to a higher count of Lactobacillus acidophilus and Bifidobacterium lactis and resulted in a higher production of lactic acid. This study lays the foundation for the biotransformation of Maple syrups into functional prebiotic ingredients.

Correlation of maple sap composition with bacterial and fungal communities determined by multiplex automated ribosomal intergenic spacer analysis (MARISA).

During collection, maple sap is contaminated by bacteria and fungi that subsequently colonize the tubing system. The bacterial microbiota has been more characterized than the fungal microbiota, but the impact of both components on maple sap quality remains unclear. This study focused on identifying bacterial and fungal members of maple sap and correlating microbiota composition with maple sap properties. A multiplex automated ribosomal intergenic spacer analysis (MARISA) method was developed to presumptively identify bacterial and fungal members of maple sap samples collected from 19 production sites during the tapping period. Results indicate that the fungal community of maple sap is mainly composed of yeast related to Mrakia sp., Mrakiella sp., Guehomyces pullulans, Cryptococcus victoriae and Williopsis saturnus. Mrakia, Mrakiella and Guehomyces peaks were identified in samples of all production sites and can be considered dominant and stable members of the fungal microbiota of maple sap. A multivariate analysis based on MARISA profiles and maple sap chemical composition data showed correlations between Candida sake, Janthinobacterium lividum, Williopsis sp., Leuconostoc mesenteroides, Mrakia sp., Rhodococcus sp., Pseudomonas tolaasii, G. pullulans and maple sap composition at different flow periods. This study provides new insights on the relationship between microbial community and maple sap quality.

Effect of the new high vacuum technology on the chemical composition of maple sap and syrup.

BACKGROUND: Techniques used to produce maple syrup have considerably evolved over the last decades making them more efficient and economically profitable. However, these advances must respect composition and quality standards as well as authenticity of maple products. Recently, a new and improved high vacuum technology has been made available to producers to achieve higher sap yields. The aim of the present study was therefore to evaluate the effect of this new system on the yield of sap and on the sap and syrup chemical composition. RESULTS: Sap yield was monitored during the 2013 and 2014 seasons for high vacuum collection systems (25-28 InHg) and compared to the control systems (20 InHg). Samples of sap and syrup were also collected for chemical analysis. During the 2013 season, a sap volume of 166.19 L/tap was recorded at 25 InHg vacuum level while the control vacuum level permitted to collect 139.47 L/tap, corresponding to a yield increase of 19.2 %. The following season, a yield increase of 38.2 % was measured when control and 28 InHg vacuum levels were compared with 118.06 and 163.13 L/tap, respectively. Results on the pH, color, flavor, minerals, sugars, organic acids, total polyphenols, total nitrogen, abscisic acid and auxin (Indol-3-acetic acid) showed no major differences between high vacuum technology and the control with values remaining within ranges previously published. CONCLUSION: Results showed that a use of high vacuum systems increased sap yield and had no major impact on the quality and purity of maple sap and syrups compared with the control systems.

A systems biology approach to explore the impact of maple tree dormancy release on sap variation and maple syrup quality.

Maple sap is a complex nutrient matrix collected during spring to produce maple syrup. The characteristics of sap change over the production period and its composition directly impacts syrup quality. This variability could in part be attributed to changes in tree metabolism following dormancy release, but little is known about these changes in deciduous trees. Therefore, understanding the variation in sap composition associated with dormancy release could help pinpoint the causes of some defects in maple syrup. In particular, a defect known as "buddy", is an increasing concern for the industry. This off-flavor appears around the time of bud break, hence its name. To investigate sap variation related to bud break and the buddy defect, we monitored sap variation with respect to a dormancy release index (Sbb) and syrup quality. First, we looked at variation in amino acid content during this period. We observed a shift in amino acid relative proportions associated with dormancy release and found that most of them increase rapidly near the point of bud break, correlating with changes in syrup quality. Second, we identified biological processes that respond to variation in maple sap by performing a competition assay using the barcoded Saccharomyces cerevisiae prototroph deletion collection. This untargeted approach revealed that the organic sulfur content may be responsible for the development of the buddy off-flavor, and that dormancy release is necessary for the appearance of the defect, but other factors such as microbial activity may also be contributing.

Analysis of plastic residues in maple sap and syrup collected from tubing systems sanitized with isopropyl alcohol.

A plastic tubing system operated under vacuum is usually used to collect sap from maple trees during spring time to produce maple syrup. This system is commonly sanitized with isopropyl alcohol (IPA) to remove microbial contamination colonizing the system during the sugar season. Questions have been raised whether IPA would contribute to the leaching of plastic residues in maple sap and syrup coming from sanitized systems. First, an extraction experiment was performed in the lab on commercial plastic tubing materials that were submitted to IPA under harsh conditions. The results of the GC-MS analysis revealed the presence of many compounds that served has target for further tests. Secondly, tests were done on early and mid-season maple sap and syrup coming from many sugarbushes using IPA or not to determine potential concentrations of plastic residues. Results obtained from sap and syrup samples showed that no quantifiable (< 1-75 µg/L) concentration of any plastic molecules tested was determined in all samples coming from IPA treated or not treated systems. However, some samples of first sap run used as a rinse solution to be discarded before the season start and that were coming from non sanitized or IPA sanitized systems, showed quantifiable concentrations of chemical residue such as ultraviolet protector (octabenzone). These results show that IPA can be safely used to sanitize maple sap collection system in regards to the leaching of plastic residues in maple sap and syrup and reinforced the need to thoroughly rinse the tubing system at the beginning of the season for both sanitized and non sanitized systems.

Level of endogenous formaldehyde in maple syrup as determined by spectrofluorimetry.

The level of endogenous formaldehyde in maple syrup was established from a large number (n = 300) of authentic maple syrup samples collected during 2000 and 2001 in the province of Quebec, Canada. The average level of formaldehyde from these authentic samples was measured at 0.18 mg/kg in 2000 and 0.28 mg/kg in 2001, which is lower than previously published. These average values can be attributed to the improved spectrofluorimetric method used for the determination. However, the formaldehyde values obtained demonstrate a relatively large distribution with maximums observed at 1.04 and 1.54 mg/kg. These values are still under the maximum tolerance level of 2.0 mg/kg paraformaldehyde pesticide residue. Extensive heat treatment of maple syrup samples greatly enhanced the formaldehyde concentration of the samples, suggesting that extensive heat degradation of the sap constituents during evaporation could be responsible for the highest formaldehyde values in maple syrup.

Spectrofluorimetric determination of formaldehyde in maple syrup.

A quick and simple method was developed for determination of formaldehyde in maple syrup. In this method, formaldehyde reacts with Fluoral P to form a complex which is chemically extracted by isobutanol and determined by spectrofluorimetry. Performance, as gauged by the limits of detection (0.16 mg/kg) and quantitation (0.21 mg/kg), recovery (>79%), and variability (1.9-16.1%, depending on fortification level and class of syrup) were superior to the current official AOAC standard method.

Maple sap predominant microbial contaminants are correlated with the physicochemical and sensorial properties of maple syrup.

Maple sap processing and microbial contamination are significant aspects that affect maple syrup quality. In this study, two sample sets from 2005 and 2008 were used to assess the maple syrup quality variation and its relationship to microbial populations, with respect to processing, production site and harvesting period. The abundance of maple sap predominant bacteria (Pseudomonas fluorescens group and two subgroups, Rahnella spp., Janthinobacterium spp., Leuconostoc mesenteroides) and yeast (Mrakia spp., Mrakiella spp.,Guehomyces pullulans) was assessed by quantitative PCR. Maple syrup properties were analyzed by physicochemical and sensorial methods. Results indicate that P. fluorescens, Mrakia spp., Mrakiella spp. G. pullulans and Rahnella spp. are stable contaminants of maple sap, as they were found for every production site throughout the flow period. Multiple factor analysis reports a link between the relative abundance of P. fluorescens group and Mrakia spp. in maple sap with maple and vanilla odor as well as flavor of maple syrup. This evidence supports the contribution of these microorganisms or a consortium of predominant microbial contaminants to the characteristic properties of maple syrup.

Seasonal and regional diversity of maple sap microbiota revealed using community PCR fingerprinting and 16S rRNA gene clone libraries.

An arbitrary primed community PCR fingerprinting technique based on capillary electrophoresis was developed to study maple sap microbial community characteristics among 19 production sites in Québec over the tapping season. Presumptive fragment identification was made with corresponding fingerprint profiles of bacterial isolate cultures. Maple sap microbial communities were subsequently compared using a representative subset of 13 16S rRNA gene clone libraries followed by gene sequence analysis. Results from both methods indicated that all maple sap production sites and flow periods shared common microbiota members, but distinctive features also existed. Changes over the season in relative abundance of predominant populations showed evidence of a common pattern. Pseudomonas (64%) and Rahnella (8%) were the most abundantly and frequently represented genera of the 2239 sequences analyzed. Janthinobacterium, Leuconostoc, Lactococcus, Weissella, Epilithonimonas and Sphingomonas were revealed as occasional contaminants in maple sap. Maple sap microbiota showed a low level of deep diversity along with a high variation of similar 16S rRNA gene sequences within the Pseudomonas genus. Predominance of Pseudomonas is suggested as a typical feature of maple sap microbiota across geographical regions, production sites, and sap flow periods.