Aroma profiles and non-destructive determination of quality parameters of Japanese plums (Prunus salicina Lindl.).

Plums with good taste, aroma and eating quality lead to repeat purchases and sustained demand. Taste
includes non-volatile compounds, e.g. sugars and acids, and has been well researched to meet the
consumers’ preferences. Plum aroma, however, has not enjoyed the same attention. Limited literature is
available on the aroma of Japanese plums and none could be found on the effects of relatively long cold
storage on the profiles. The main aim of this study is to investigate the changes in aroma compounds of
Japanese plums throughout maturation and ripening and the effects of commercial cold storage regimes.
Near infra-red (NIR) spectroscopy was also evaluated as a non-destructive method to determine plum
quality parameters aimed at minimising sample variability.
In Paper 1, NIR spectroscopy was used to develop prediction models for total soluble solid (TSS), total
acidity (TA), sugar-to-acid ratio, firmness and weight in three cultivars (Pioneer, Laetitia and Angeleno)
and a multi-cultivar model. Samples were collected for seven consecutive weeks and repeated over two
seasons. TSS results showed excellent predictability (R2 = 0.817-0.955; RMSEP= 0.453-0.610 % Brix)
but the TA models did not perform well. The sugar-to-acid ratio models had results comparable to that of
TSS. Both the firmness and weight models had acceptable results. The models of ‘Pioneer’ and ‘Laetitia’
had a better predictability capacity than the ‘Angeleno’ model. Although the multi-cultivar models
outperformed the single cultivar models on R2 values it had higher prediction errors. The robustness of all
the TSS, TA and firmness models is high in terms of seasonality, range and cultivar.
Papers 2 and 3, the main focus of the study, are concerned with the aroma profile dynamics of Japanese
plums. HS-SPME was used in both papers to extract the aroma compounds followed by GC-TOFMS for
separation and identification. In Paper 2, the aroma volatile compounds of three cultivars (Pioneer,
Laetitia and Angeleno) were determined for a seven week period including samples from three maturity
stages (immature, harvest and tree-ripe). A total of 35 compounds were identified of which ten were
generic. Each cultivar had five unique compounds resulting in different aroma profiles for each of the
maturity stages and distinct separation patterns using discriminant analysis.
The study was extended in Paper 3 where the aroma volatile compounds of six cultivars (Pioneer,
Sapphire, Laetitia, Songold, Larry Anne and Angeleno) and one plumcot (Flavor King) were determined at
three functional stages (commercial harvest, tree-ripe fruit and cold stored fruit). A total of 62 compounds
were identified and classified into three groups (‘unique’ (31), ‘generic’ (11) and ‘frequent’ (20)) based on their frequency of occurrence. The aroma profiles of ‘Larry Anne’ and ‘Flavor King’ are the most affected
by cold storage conditions and ‘Pioneer’ appears to be the least affected. All the cultivars have
significantly different aroma profiles at all three of the functional stages with ‘Sapphire’, ‘Larry Anne’ and
‘Flavor King’ showing the largest differences. ‘Flavor King’, a plumcot, presented a ripe aroma profile that
was much diverged from that of the true plums.