Finding
Practical applications of the results of such a study might be to provide an efficient tool to strawberry plant breeders or to allow labelling of strawberries to promote their sensory quality.
Paper
MEASUREMENT OF THE SENSORY QUALITY OF STRAWBERRIES
Abstract
s The objectives of the project were to test rapid methods to objectively measure the sensory quality of commercial strawberries and to define a model for their quality assessment. Variations of the sensory quality caused by different cultivars were present at the 10 consumer tests from 1998 to 2002. The relationship between consumer’s appreciation of these cultivars and the laboratory measurements proved that the sensory quality of strawberries is rapidly and objectively measurable by analysing the soluble solid content (°Brix) of the fruits. The analysis of the total volatile compounds of the fruits was significantly related to the consumers’ appreciation for merely a few tests. Further investigations are required to verify this relationship. However, the measurements of titrable acidity and firmness as well as the °Brix/acidity ratio were not efficient to reflect the consumers’ opinion. The seven consumer tests with categorisation from 1999 to 2002 showed different regression lines between the sensory quality of strawberries and their soluble solid content (°Brix). This indicated that it tends to be difficult to set the same °Brix as a quality attribute to obtain consumer satisfaction every year or every season of the year. Nevertheless, a provisional model for the assessment of sensory quality of intact, undamaged and not overripe strawberries relative to their soluble solid content (°Brix) was suggested. INTRODUCTION Health and enjoyment are the two main reasons for eating fruits. However, the sensory quality of commercial strawberries is often negatively criticised. During the past years, the external appearance, storage and transportation tolerance as well as agronomic parameters of commercial strawberries have considerably improved contrary to their sensory quality. To improve and promote the sensory quality of strawberries, a project was started in 1997 with the collaboration of the School of Engineering Valais (HEVs), the Office of Agriculture of the Canton of Valais and the Union of Migros Co-operatives, the biggest chain of food stores in Switzerland. One of the major objectives was to determine methods to objectively and rapidly measure the sensory quality of strawberries. A further goal was to define a model for the assessment of the quality of strawberries. Practical applications of the results of such a study might be to provide an efficient tool to strawberry plant breeders or to allow labelling of strawberries to promote their sensory quality. MATERIALS AND METHODS Standard hedonic consumer test: 10 consumer tests were performed with more than 100 persons per test in several regions of Switzerland. Consumers commented on their overall appreciation of the sensory quality of 4 to 6 strawberries cultivars on a scale from 1 to 9 (1= very bad, 3 = bad, 5=medium, 7=good, 9=excellent). Afterwards, a sample of 500g (a basket) per cultivar was analysed by instrumental methods. Only intact, undamaged and not overripe strawberries were used in these consumer tests Hedonic consumer tests with categorisation: Strawberries were cut into two parts. Proc. Int. Conf. Quality in Chains Eds. Tijskens & Vollebregt Acta Hort. 604, ISHS 2003 354 Consumers eat and appreciated one half and the other half was classified according to the score obtained (1 – 9). The pooled samples were homogenised and subjected to measurements in the laboratory (500 g per score). This method is more adapted for developing a model for the assessment of the quality because the same fruit sample could be analysed by consumers and by instrumental methods. Instrumental methods: The fruit samples were mashed and soluble solid content (refractometer Atago, PR-1, Kunzmann, Switzerland), and titrable acidity (Mettler DL 25, Mettler-Toledo, Switzerland) were analysed. The fruit’s firmness was determined using a Kramer’s shear cell operated by a shear test machine (Versa Test + Advanced Forces Gauge, Memsin, Brutsch & Rueger, Zurich, Switzerland) in 1998 and 1999. From 2000 firmness was measured with a hand-penetrometer (Durofel 50). To measure the total volatile compounds 50 g of mashed strawberries were mixed with 50 g of a saturated ammonium sulphate solution. This mixture crystallised in a dish (diameter of 100 mm and height of 30 mm) and was placed in the headspace flask (volume 2500 ml) for 5 minutes at 25°. Then the volatile compounds were collected during 5 minutes with the SPME (Solid Phase Micro Extraction) fibre PDMS (polydimethylsiloxane; Supelco Co., Bellefonte, PA, USA). A mixture of 1-methoxy-2propyl-acetate (1 mg/kg), 2 methyl ethyl ketone (1 mg/kg) and butanol (1 mg/kg) was used as an external standard. A GC measured the sum of the absorbed volatile compounds as previously reported by Azondanlou et al. (1999) and Azodanlou (2001). In 2001 and 2002, a modified procedure was adapted: A mixture of 2 g of mashed strawberries and 2 g of a saturated ammonium sulphate solution was put in a vial (volume of 40 ml) for 35 minutes at 25°. Then the total volatile compounds were measured as mentioned above. RESULTS The different cultivars appreciated by consumers obtained different average sensory quality scores (Fig. 1). However, the evaluated fruits per cultivar were heterogeneous. The consumers’ appreciation of sensory quality of strawberry was strongly related to its soluble solid content (°Brix) in 80 % of the standard consumer tests tests (Table 1 and 2). However, the analysis of the total volatile compounds was related to the consumers’ score only in 20 % and that of firmness and °Brix/acidity ratio only in 10 % of the tests. Measurements of the titrable acidity were not associated with the consumers’ rating of quality. The sensory quality scores (form 3 to 9) evaluated by consumers in the tests with categorisation was strongly related to the soluble solid content (°Brix) for all tests and to their total volatile compounds for 5 of 7 tests (Table 3 and 4). However, there was no significant correlation for titrable acidity. The regression lines between the consumers’ quality appreciation of the fruits and the strawberries’ soluble solid content were different for each consumer test with categorisation (Fig. 2). These relationships allowed an approach for defining a provisional model for the assessment of strawberry quality by calculating the average soluble solid content of the fruits per sensory quality class: excellent sensory quality around 9.1 °Brix; good sensory quality around 8.1 °Brix, medium sensory quality around 7.3 °Brix and bad sensory quality around or lower than 7.0 ° Brix (Table 5). DISCUSSION The first objective was to test rapid methods to objectively measure the quality of the fruits. A rapid method to determine objectively the sensory quality of strawberries is the measurement of the soluble solid content of the fruits with a refractometer (°Brix). Alavoine and Crochon (1989) also revealed that sugar content (°Brix) was strongly related to the quality of strawberries. The measurements of the total volatile compounds of strawberries seemed to be less accurate and more time consuming. Further investigations are required to verify the significance of this method for practical applications. However, titrable acidity, °Brix/acidity ratio and firmness did not seem to be
Authors
C. Carlen, A. Ançay
Journal
Journal name not available for this finding