Pascal Schlich

Bitterness and astringency of flavan-3-ol monomers, dimers and trimers†

Intensity of astringency and bitterness of seven flavonoid compounds was evaluated by a time-intensity (TI) procedure. Eighteen trained judges rated intensity continuously from ingestion, through expectoration at 10u2009s until extinction of the sensation. The seven stimuli included two flavan-3-ol monomers, (+)-catechin and (−)-epicatechin, three dimers and two trimers synthesised from catechin or epicatechin by condensation with (+)-dihydroquercitin. As the degree of polymerisation increased, maximum bitterness intensity (Imax) and total duration (Ttot) decreased whereas astringency Imax increased. The monomers were significantly higher in bitterness at Imax than the dimers, which were significantly higher than the trimers. Astringency Imax of the monomers was lower than the dimers or trimers, although no significant difference was found in Ttot among the polymer classes. The bond linking the monomeric units had an influence on both sensory properties. The catechin-catechin dimer linked by a 4→6 bond was more bitter than both catechin-(4→8)-catechin and catechin-(4→8)-epicatechin. Astringency was affected by both the specific linkage and the identity of the monomeric units with the dimer, catechin-(4→8)-catechin, being lower in astringency than either catechin-(4→6)-catechin or catechin-(4→8)-epicatechin. n n© 1999 Society of Chemical Industry

Internal and external mapping of preferences for commercial lager beers: comparison of hedonic ratings by consumers blind versus with knowledge of brand and price☆

Abstract The individual preferences of 170 consumers in six categories of age (20s, 30s, 40s) and gender (men, women) for 24 domestic, imported or specialty lager beers, tasted first blind and then with knowledge of brand and price, were investigated by preference mapping techniques. Internal preference mapping revealed differences in the preferences of consumers, with some consumers preferring domestic or ice beers, and others preferring specialty or imported beers. Hedonic ratings changed significantly from the blind to the informed tasting condition, particularly for consumers in their twenties, thereby documenting the significant role of non-sensory variables in the formulation of a hedonic judgement by the consumer. In an external preference map relating the consumers hedonic ratings to the first two principal components of a principal component analysis of descriptive ratings for the 24 beers, 75% of the consumers were fitted by the vectorial, circular, elliptical (with maximum or saddle point) or quadratic AUTOFIT models, at the required minimum level of significance ( P ⩽ 0.25 for wrongly not simplifying the model, and P ⩽ 0.25 for wrongly selecting a consumer). This improvement over previous studies is credited to the high number of samples (24) in the design, and to the large differences in sensory properties among samples.

Uses of change-over designs and repeated measurements in sensory and consumer studies

Abstract The paper illustrates two statistical methods, the design and analysis of sensory experiments taking into account the effects of serving order and previously assessed treatment and the analysis of experiments with time repeated measurements. Change-over design experiments balance both presentation order and carry-over effects. The proper analysis of variance allows the testing of these effects and the estimation of product means adjusted for carry-over effect. Repeated measurements occur when groups are being compared over time. Either a corrected split-plot or a multivariate analysis of variance (MANOVA) with measurements at different times forming the variable should be adopted to allow proper tests for the time effect and for its interaction with the group effect. The usefulness of change-over designs with an appropriate analysis and repeated measurement analysis will be demonstrated using sensory experiments involving trained assessors and consumers.

Risk tables for discrimination tests

Abstract Duo-trio and triangle test are often used in the food industry for the purpose of declaring two products non-distinguishable. In that situation, it is much more important to control the power of the test rather than the type 1 error risk. This paper makes available by e-mail a SAS ® macro, called BINRISKS, for computing type 1 and type 2 risks for any one-tailed binomial test and for any level of the percentage above chance to be detected. Using this macro, two sets of tables have been compiled. The first table includes for any total number of responses below 50, for any number of correct responses and for three levels of the percentage above chance to be detected, the corresponding type 1 and 2 risk values. The second table indicates the minimum total number of responses and the associated number of correct responses required to achieve several combinations of risks of types 1 and 2 for six different percentages above chance.

Using repeated ingestion to determine the effect of sweetness, viscosity and oiliness on temporal perception of soymilk astringency

Abstract Astringency is a persistent sensation which increases upon repeated ingestion. To evaluate the effect of viscosity, sucrose and oil on perception of astringency during consumption of soymilk, a sequential sipping time–intensity (TI) procedure was utilized. For each soymilk, judges sipped the first of four ingestions and initiated the continuous recording of astringency intensity. Each sip was expectorated at 10 s after ingestion, and sipped 10 s after expectoration of the previous stimulus. After the fourth sample, judges rated astringency for 30 s. Traditional TI parameters, as well as rate of onset for each sip and increase in maximum intensity per sip were extracted from the TI curves. Maximum astringency (IMAX) increased significantly with successive sips as did the astringency at the time of sipping. Time to IMAX decreased from sip 1 to 3, but was longer for sip 4, which may be an artifact of the rapid test pace. Although addition of 60 g l −1 canola oil had no affect on astringency, adding 40 g l −1 sucrose or increasing viscosity by 5 cp with CMC significantly lowered all astringency parameters. The reduction in astringency by CMC may result from restoration of salivary lubrication and in part by chelation or hydrogen bonding of CMC to the astringents reducing their ability to bind to salivary proteins. The reduction in astringency produced by sucrose is more probably due to a cognitive process. ©

Handling replications in discrimination tests

We give in this paper an easy to use and statistically sound way of handling replications in discrimination tests based on a concept called overdispersion. The overdispersion is easily calculated by hand for any discrimination testing setup. And since the method simply amounts to correcting the total number of observations, and similarly the overall response, by the overdispersion, we can use any standard technique, table or software on the corrected numbers to perform a statistical test for difference, for similarity, power calculations, controlling risk I and risk II, etc. We also include a general discussion of the replicated discrimination testing situation, and some examples to illustrate how to use the method. The SAS® macro REPRISKS that handles all computations is available by e-mail: schlich@arome.dijon.inra.fr.

Correspondence analysis in sensory evaluation

Abstract Correspondence analysis is a technique which has been little used by sensory scientists for sensory evaluation data. It is a technique which has similar objectives to principal component analysis and generalized Procrustes analysis in that it reduces the dimensionality of data to a more easily interpretable number of dimensions. In addition, it has been argued by advocates that it is more correct to use correspondence analysis with sensory data due to its often categorical nature. This paper aims to illustrate the use of correspondence analysis in sensory evaluation, and compares the results with those obtained from principal component analysis and generalized Procrustes analysis.

Comparison of odour sensory profiles performed by two independent trained panels following the same descriptive analysis procedures

Odour sensory profiling of 28 associations of cheese ripening micro-organisms was performed by two panels of 10 assessors on two different sites. Sample preparation, training protocols and references, tasting procedures and scoring were similar in the two laboratories. Panel 2 used 10 attributes and panel 1 used these terms plus 4 extra descriptors. Analysis of variance and multivariate methods (canonical variate analysis, generalised procrustes analysis and STATIS) exhibited differences between assessors within a panel and between panels concerning the use of the scoring scale and the strength of product discrimination by attribute. Panel 1 was more sensitive to fruity notes and panel 2 to sulphury odours. However, a good overlap in the separate and pooled analyses suggested the same sample clustering in three main groups and showed that the 2 panels gave consistent results.

Comparison of wine discrimination with orthonasal and retronasal profilings. Application to Burgundy Pinot Noir wines

Two sensory spaces, corresponding to the same wine sample profiled by nose (BN) and profiled by mouth (BM), were compared. The similarity between the two maps of product differences were measured by multivariate analysis, showing a good agreement and comparable product discrimination by the panel in the two modes, slightly in favor of BN discrimination. The superiority of one particular mode was not established from the comparison of individual performances BN versus BM, but differences between panelists and between descriptor use were found. Two-way canonical variate analysis of BN minus BM scores was also performed: the results revealed that panelists had higher influence than products in the differences observed between the two modes.

Amylase production in submerged culture using principal component analysis

Abstract The aim of our work was to study the production of α-amylase and glucoamylase in submerged culture by a species of Aspergillus niger screened for its high amylase activity. Statistical analysis was not used to optimize fermentation conditions but it was employed in a new approach to describe the culture behaviour. Principal component analysis (PCA) was applied to describe the influence of three agitation speeds on the rate of amylases synthesis and on the evolution of other indirect growth factors. The results of this analysis showed that the oxygen transfer at various agitation speeds affected the levels of enzymes, their production rates and the CO 2 production rate (indirect measurements of growth rate). Maximal α-amylase synthesis was observed at the lower agitation rate whereas the glucoamylase synthesis was maximum at the intermediate agitation rate.