Detection Thresholds for 2‐Isopropyl‐3‐Methoxypyrazine in Concord and Niagara Grape Juice

Abstract

2-isopropyl-3-methoxypyrazine (IPMP) is the compound responsible for the off-flavor known as ladybug taint, which occurs when Harmnonia axyridis beetles become incorporated with the grapes during juice processing. It is also an important grape-derived component of juice flavor in some varieties. The main objective of this study was to determine the orthonasal (ON) and retronasal (RN) detection thresholds for IPMP in juice. The ASTM E679 ascending forced choice method of limits was used to determine detection thresholds for 26 individuals in Concord and Niagara juices. Group best estimate thresholds (BETs) averaged 0.93 ng/L and were 50% and 21% higher in Concord than in Niagara juices for ON and RN evaluation, respectively. Group BETs for IPMP (ng/L) for Concord were ON: 1.11; RN: 1.02 and for Niagara were ON: 0.74; RN: 0.84. Variation in individual detection thresholds was observed, although familiarity with ladybug taint was not associated with individual threshold values. We conclude that humans are very sensitive to IPMP in juice, and that detection thresholds are more strongly influenced by grape variety than evaluation mode. These results may assist juice producers in establishing tolerance levels for IPMP in juice affected by ladybug taint or derived from grapes of suboptimal ripeness.

Ladybug (Coccinellidae) taint in wine

“…The detection threshold for IPMP in red wine is 1-2 ng/L (Maga, 1989;Pickering et al, 2007a) and 0.3-1.6 ng/L in white wine (Pickering et al, 2007a). Similar thresholds have been reported in grape juices (Pickering et al, 2008c). Factors mediating IPMP threshold in wine include mode of evaluation (ortho-vs retro-nasal assessment), wine style and familiarity with the odorant (Pickering et al, 2007a).…”

Impact of Multicolored Asian Lady Beetles on the Sensory Properties of Concord and Niagara Grape Juice

“…When MALB were added to Frontenac wine grapes, Galvan and others (2007) found the average aroma threshold reported was 1.9 MALB/kg grapes. With regard to differences between the 2 grape juices, Pickering and others (2008) also reported a lower orthonasal and retronasal threshold in Niagara grape juice compared to Concord grape juice for 2‐isopropyl‐3‐methoxypypyrazine, a compound thought to be the major contributor to MALB‐taint. The difference in thresholds between the 2 juices was thought to be due to the more intense aroma associated with Concord grape juice, an aroma attributed to the presence of methyl anthranilate.…”

“…Pyrazines are a component of the hemolymph, a fluid released by the MALB when they are rushed or disturbed (Galvan and others 2008). In grape juice, the detection threshold of 2‐ isopropyl‐3‐methoxypyrazine, a major contributor to MALB‐taint, was determined (Pickering and others 2008). In Concord grape juice, the orthonasal and retronasal threshold was 1.11 and 1.02 ppt, respectively, while for Niagara grape juice, the threshold was 0.74 and 0.84 ppt, respectively.…”

Aroma profile of Niagara grape juice contaminated with multicoloured Asian lady beetle taint using gas chromatography/mass spectrometry/olfactometry

“…, 2008) and grape juice (Ross et al. , 2007; Pickering et al. , 2008) have been documented in the literature.…”

“…The multicoloured Asian lady beetle (MALB) (Harmonia axyridis: Coleoptera: coccinellidae) was originally introduced into the USA as a method of biocontrol for aphids and other soft bodied insects (Nalepa et al, 1996). However, the establishment of MALB populations and the off-aromas associated with the presence of MALB in wine grapes (Galvan et al, 2007), finished wines (Pickering et al, 2004;Galvan et al, 2008) and grape juice (Ross et al, 2007;Pickering et al, 2008) have been documented in the literature. In 2001, the presence of MALB taint resulted in the disposal of a million liters in Ontario, directly causing the Ontario wine industry a multi-million dollar loss in sales.…”