ACW | 2012
Introduction
Apple juice belongs to the most frequently consumed types of fruit juices. The occurrence of off-flavour is regarded as a problem as it is supposed to diminish the product quality significantly and may lead
to consumers rejections. In apple juice production, Alicyclobacillus acidoterrestris is proven being an important spoilage bacteria. It is of special interest to the fruit processing industry in general, as traditional processing techniques such as pasteurisation do not deactivate the spores. Although not harmful for the consumers, it might influence the sensory product profile.
The bacteria produces certain aroma compounds, one of which is guaiacol - reminiscent of a medicinal, smoky, fatty, barbecue and bacon-like aroma. It is difficult to keep it off the production chain. Apple juice producers are hence sensitive towards this sensory influence and envisage consumers’ disliking. Although most producers declare it as off-flavour, some preliminary investigations showed not a consequent disliking of the infected apple juice. What, if consumers even prefer it? We are trying to answer this using preference testing.
Material and method Products & Subjects
Participants have been presented two apple juice samples. They were asked to choose the preferred sample. One sample being a pasteurized standard brand
“Rio d’ Oro” from Aldi Switzerland, made of 100% apple juice. The second sample was the same apple juice inoculated by Alicyclobacillus acidoterrestris.
Measurement identified a guaiacol concentration of 2.2 µg/l, just above olfactory recognition threshold. Data evaluation was made using a two-sided, directional difference test atα=5%.
Results & Discussion
Overall, results indicate no significant preference between the two apple juice samples at an α-error of 5% across all participants. When splitting data into age groups and background (consumer/producer) of participants, some consumer group detected a significant difference. The consumers aged 60 and above (n=29) had a significant preference for the juice without infection. Interestingly not the apple juice producers. The olfactory recognition threshold of guaiacol in apple juice is stated in literature 2.0 – 2.23 µg/l, however the odour detection threshold is stated as 0.57 – 0.91µg/l. The sample inoculation was therefore clearly above detection threshold level.
Participants commented the infected apple juice sample as having less sweetness, more mouthfeel properties and being more complex in overall aroma.
Conclusion
Often untypical aroma compounds are regarded as off- flavours which hence are anticipated with consumers disliking. Some untypical aroma compounds can, within a certain concentration however, even lead to preferences by adding the aroma profile more complexity. Further research needs to investigate a concentration maximum, as very high levels of guaiacol might lead to a disliking relationship. A second study axis will also include different concentrations of guaiacol, clearly above odour recognition threshold level to get more insights whether the producers’s problem – the spoilage with Alicyclobacillus acidoterrestris – is also a consumers’
problem.
Literature
B. Siegmund, B. Pollinger-Zierler (2006): Odor thresholds of microbially induced off- flavor compounds in apple juice. Journal of Agricultural and Food Chemistry, 54 (16), pp. 5984–
5989
Pilar Ruiz Pérez-Cacho et al. ( 2011) GC–MS quantification and sensory thresholds of guaiacol in orange juice and its correlation with Alicyclobacillus spp.. Food Chemistry , 129, (1), pp. 45–
50
B. Zierler et al.(2004): Determination of off-flavour compounds in apple juice caused by microorganisms using headspace solid phase microextraction–gaschromatography–mass spectrometry / Analytica Chimica Acta 520 ,3–11
When Off-flavours have no effects on liking – The Case of Apple Juice
Christine Brugger*, Geneviève Clara Nicol, Jürg Gafner
Agroscope Changins-Wädenswil Research Station ACW, CH-8820 Wädenswil; www.agroscope.ch
Outlook
As producers claim it being the number one problem in apple juice production we suggest to validate the data in:
*different product matrices (different sweetness and sourness levels)
*different aromatic apple varieties
*different carbonation levels
to study the effect of guaiacol on sensory perception.
Figure 3: Apple juice samples Figure 4: Product relationship of tasters Figure 2: Age distribution (n=203) Figure 1: Gender split among participants
