Flavour formation in the coffee substitute 'lupin coffee' related to the formation of acrylamide

Abstract

A coffee substitute derived from sweet lupins (Lupinus angustifolius L.) was investigated for the first time with regard to the impact of the roasting process on flavour formation, acrylamide generation, and amino acid behaviour. Roasting was carried out batchwise at temperatures between 98 °C to 220 °C. 55 volatile compounds were semi-quantified using headspace SPME GC-MS. Maillard reaction products, particularly substituted pyrazines and furans, constituted the majority of the volatiles formed. The flavour of "lupin coffee" was described as strongly roasted and reminiscent of coffee, though less complex than traditional coffee. Flavour development became evident at temperatures of 195 °C and above. The highest acrylamide concentration detected was 111 μg/kg at 220 °C which is considerably below the EU benchmark levels established for coffee substitutes. This work provides a solid foundation for future investigations aimed at minimising process contaminants while preserving the desired flavour.

Keywords: Acrylamide; Amino acids; Coffee substitute; Flavour formation; Lupin seeds (Lupinus angustifolius L.); Roasting.

Graphical abstract

Fig. 1

Temperature on the surface of the lupin seeds as a function of the air stream; red dots indicate the sampling points. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Fig. 2

Sample material obtained from different roasting steps, Fig. 2a: ground lupin seeds; Fig. 2b: French press brews.

Fig. 3

Principal component analysis results (PC1 vs PC2, observations plot; corresponding analysis, p < 0.05) based on the results from sensory evaluation (OEQ) of ground lupin seeds of different roasting stages; n = 13.

Fig. 4

Principal component analysis results (PC1 vs PC2, observations plot; correspondence analysis, p < 0.05) based on the results from sensory evaluation (OEQ) of French press brews produced from lupin seeds of different roasting stages; n = 13.

Fig. 5

Principal component analysis results (PC1 vs PC2, biplot; Pearson correlation, p < 0.05) showing the correlations between sensory data of ‘lupin coffee’ infusions, the volatile compounds and acrylamide in the course of the roasting process; blue: observables (samples taken at different roasting temperatures), black: sensory attributes; red: volatiles, highlighted in yellow: acrylamide. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Fig. 6

Concentrations of 19 proteinogenic amino acids in the course of the roasting procedure, cysteine was not detected in the lupin seeds;”RM” raw material, n = 2; One-way ANOVA followed by post-hoc pairwise comparison using Tukey's Honestly Significant Difference (HSD) test control (p = 0.05) to check for differences between single samples. For amino acids whose concentration was below LOQ, a concentration of (LOQ + LOD)/2 to be able to calculate ANOVA. ^{A, B, C, D} Different superscript letters indicate statistically significant differences (p < 0.05) among the different roasting stages of the lupin samples.

Fig. 7

Development of acrylamide in the course of the roasting process in comparison with the degradation of asparagine and glutamine (n = 2); acrylamide concentrations red bars in μg/kg (different letters indicate statistically significant differences between acrylamide levels, p < 0.05), asparagine concentration blue line in mg/kg, glutamine concentration green line in mg/kg(information on statistical differences are given in Fig. 6). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)