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 | | THE BITE OF CONFECTIONERY COATINGS | | | International Food Ingredients | | 29/05/2008 | | | Geoff Talbot, The Fat Consultant
Kevin W. Smith, Unilever Research
Hennie Slager, Loders Croklaan
What are the first sensory characteristics you look for in a bar of chocolate? Appearance is probably the first thing we are aware of – whether the chocolate has a good gloss, whether or not it has bloomed. Then, perhaps aroma as we open the wrapper on the bar. But when we first bite into the chocolate we become immediately aware of how hard the chocolate is, particularly what we have termed to be its ‘hardness at first bite’. This sensory attribute is an important one irrespective of whether it is chocolate or a compound coating and, certainly, there are differences between all of these products. When milk fat is present the coating is softer; a non-lauric compound coating tends to be less brittle than a lauric compound coating. All these differences are apparent in the ‘hardness at first bite’.
How can we predict, then, such an important sensory characteristic? Over the years various researchers have looked at this issue. Tscheuschner and Markov (1989) found that the compression strength of chocolate decreased as the fat level increased. Guinard and Mazzucchelli (1999) studied nine milk chocolates and found that there was a correlation between hardness of the chocolate and both sugar and fat levels. Both of these studies looked at the effects of fat level on hardness, but an equally important factor is the effect of fat type and, in particular, the effect of the proportion of solid fat in the coating on hardness. Good correlations have been found between the level of solid fat in a coating and its hardness as measured by both penetration and texture analysis. This article, however, describes the correlations between these instrumental measurements and hardness as perceived by a trained sensory panel.
Coatings
Coatings fall into three main types (Talbot, 2007) – chocolate, non-lauric compound coatings and lauric compound coatings. To keep the number of samples to a manageable number as far as panellists were concerned we looked at eight different coatings, each with different melting profiles. Five of these were based on non-lauric, COUVA™ compound coating fats with gradually decreasing levels of solid fat (NL1-NL5); one was based on a lauric CLSP™ compound coating fat; the other two were cocoa butter based (CB), one without milk fat, the other with milk fat (CBMF).
When instrumental methods were compared (Talbot, Smith, Slager, 2008) we found that there was a good correlation between them when only the non-lauric compound coatings were considered, although the lauric coating also fitted reasonably well with these. However, the two cocoa butter coatings were completely different and needed a different, separate correlation. We considered that this was due to the crystalline nature of cocoa butter producing a coating which had a greater hardness at a particular solid fat content than did the two types of compound coating.
Sensory evaluation
People eat chocolate and coatings in different ways so, in order to get comparability between results, we trained panellists in how to bite initially into these products. This meant training them to first move the piece of chocolate to the back of the mouth and on to the side teeth (without significant melting of the chocolate) and then biting into it.
To compare the sensory results with instrumental techniques three methods were used – (1) solid fat content, (2) penetrometry, (3) hardness using a Brookfield LFRA Texture Analyser. Solid fat contents were measured between 15°C and 35°C on (a) the fat itself solidified directly in a glass NMR tube, (b) a sample taken from a moulded bar of the fat, and (c) a sample taken from a moulded bar of coating. Penetrometry and hardness measurements were made on samples stored at 15°C, 20°C and 25°C. Sensory analysis was carried out on samples stored at 20°C. The common temperature, therefore, between all of these measurements was 20°C. Although we shall concentrate on correlations between measurements made at 20°C, we did also make correlations at other temperatures and, where appropriate, reference will be made to these.
Correlations
Sensory hardness and solid fat content
The simplest instrumental measurement to make is that of solid fat content on the fat phase because then it is unnecessary to make the coatings or to mould bars of any form – so a good correlation with solid fat content would have been an ideal result.
Unfortunately, and somewhat surprisingly, the only solid fat content measurement to correlate with the sensory hardness scores at 20°C was that measured on the coating bar at 25°C. If there was going to be a correlation we did, at least, expect that it would be with measurements made at the same temperature. Correlations were slightly better if only the five non-lauric (NL) blends were considered but, even then, the best correlations were at unexpected temperatures, e.g. solid fat content at 32.5°C with sensory hardness at 20°C. A possible reason for this better correlation with solid fat contents measured at higher temperatures could be the time the sample stays in the mouth during which it will start to warm up.
Sensory hardness and penetration
There were good correlations between sensory hardness and penetration measurements made on both fat and coating bars at 15°C and 20°C but not at 25°C. The softest non-lauric system (NL5) was an outlier when the penetration measurements themselves were used (Figure 1) but was less of an outlier when a logarithmic relationship was used.
Sensory hardness and Brookfield LFRA hardness
It was not possible to obtain a linear correlation between sensory hardness and Brookfield LFRA hardness for either the fat bars or the coating bars. This is not to say that the two parameters do not correlate because we found it possible using non-linear regression analysis to fit an S-shaped curve
Summary
Instrumental ways of measuring a coating’s hardness such as penetrometry and texture analysis showed good correlations with ‘hardness at first bite’ from a sensory panel. There were differences between the two techniques with texture analysis being better able to accommodate the results of softer coatings, though in a non-linear fashion.
In our earlier work comparing the instrumental methods themselves it was found that cocoa butter-based blends behaved differently from the non-polymorphic non-lauric and lauric systems making a single correlation impossible. However, when sensory hardness is compared with instrumental penetration and texture analysis measurements there is no distinction between the different types of coating thus allowing a single, simple correlation to be made.
This means that, although it is not possible to predict sensory hardness from the solid fat contents of the fat phase of a coating, it is possible to predict it from other instrumental measurements of hardness, particularly texture analysis.
This will allow the confectionery and bakery industry to better control the quality of coatings in terms of this sensory attribute simply by instrumental means without having to resort to the expense of training and using panellists.
References
Guinard J-X, Mazzucchelli R (1999) – ‘Effects of sugar and fat on the sensory properties of milk chocolate: descriptive analysis and instrumental measurements’ – J. Sci Food Agric. 79 1331-1339
Talbot G (2007) – ‘The changing face of coatings’ – International Food ingredients, August/September, 56-57
Talbot G, Smith KW, Slager H (2008) – ‘Can coating hardness be predicted?’ – in press
Tscheuschner H-D, Markov E (1989) – ‘Instrumental texture studies on chocolate. III Compositional factors influencing texture’ – J. Texture Stud. 20 335-345 | |
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