Chloroplast Fluorescence can be Used as a Nondestructive Tool for Quality Measurements of Stored Apple Fruit

J. Song(1), P. R Armstrong(2), R. M. Beaudry(3)

(1,3) Department of Horticulture, Michigan State University, East Lansing MI 48824, U.S.A.
(2) Dept. Biosystems and Ag. Engineering, Oklahoma St. Univ., Stillwater, OK 74078-0497, U.S.A.

Segregating high- and low-quality fruit through some form of sorting procedure is an important component of quality control of the final packout. Chlorophyll fluorescence is induced by direct excitation of chlorophyll molecules of photosystem II by light and their immediate relaxation, which has been used as a measure of chloroplast function and, indirectly, as a measure of whole plant and plant organ physiological status. This suggests chloroplast fluorescence could be used to predict or detect the maturity and/or senescence of apple fruit. Our objective was to determine if there was a relationship between chloroplast fluorescence and standard quality indices of MT firmness and ground color during fruit senescence immediately after storage and during an accelerated aging period after storage.

Result

All fluorescence parameters declined with time as apple fruit were maintained at 22°C in air. Fv/Fm was found to correlate well with firmness for 'Red Delicious' fruit. Fo and Fm correlated with yellow coloration of 'Golden Delicious' fruit (data not shown). The Fv/Fm value was consistently higher for controlled-atmosphere (CA) stored fruits than for regular-air (RA) stored fruits. When CA and RA stored 'Law Rome' fruit were combined and a Fv/Fm value of 0.685 was used re-segregate fruit from the two storage regimes, Re-segregation was achieved with 75% accuracy (Fig. 1).

Conclusion

The accuracy, speed of assessment and light-based nature of fluorometry suggest it may have some practical use as a tool for sorting apple and other chlorophyll-containing fruit on commercial packinglines.
  1. Fluorescence decreased during the period of poststorage, which indicates a potential relationship between fluorescence and fruit senescence.
  2. Firmness and fluorescence declined synchronously. The implication is that fluorescence may serve as a correlative measure of fruit firmness or fruit firmness retention and, perhaps, fruit condition or ability to retain condition.
  3. Fluorescence and background color for 'Golden Delicious' fruit give rise to the possibility that chloroplast fluorescence can be used as a practical tool to measure fruit background color.
  4. The use of Fv/Fm successfully to segregate CA- and air-stored fruit. Fm or Fv/Fm can be put to practical use by the fruit industry.
  5. Fluorescence has good potential to provide information needed to assist size and color sorting systems in obtaining a higher quality, more competitively positioned packout for apple fruit.

Fig.1. Fluorescence (Fv/Fm) and MT-firmness for 'Law Rome' apple fruit from CA storage (1.5% O2, <2.0% CO2) and RA storage for 4.5 months (a) and segregation accuracy using a Fv/Fm threshold (b). Accuracy reflects percent RA and CA fruit that were correctly segregated.