# Comprehensive Assessment of the Dynamics of Banana Chilling Injury by Advanced Optical Techniques
## 1 Introduction
(2011) [16] suggested that membrane degradation due to chilling-enhanced cellular oxidative stress [11; 17] results in the loss of cellular compartmentation and the mixing of phenolic substances. Then, PPO might contribute to brown and black discolorations of the peel tissue. The general finding that symptoms of CI may become visible only after transfer to shelf life conditions (see above) has also been reported for banana [11; 12; 26]. However, other reports indicated CI occurrence during storage at chilling temperatures [6; 8], even if these are moderate [10; 31]. The reason(s) for this discrepancy is(are) not clear but may depend on storage or experimental conditions, e.g., temperatures used, on developmental stage or on provenance of fruit. Nevertheless, this issue certainly needs closer examination. Membrane damage, increased permeability and impaired compartmentation seem to be the basic mechanisms of CI [2; 4; 32]. This, in turn, renders photosynthesis an early and major target of chilling stress in photosynthetically active fruits and vegetables. Consequently, chlorophyll-fluorescence analysis (CFA) [33; 34; 35] provides a useful tool to rapidly and noninvasively evaluate the development and the severity of CI symptoms [36]. CFA and particularly the potential maximal photochemical efficiency of PSII (\(F_{\rm v}/F_{\rm m}\)), has indeed been used widely to monitor the concomitant decline in the efficiency and/or the integrity of photosystem II (PSII) as well as the often-subsequent degradation of chlorophyll molecules [12; 37; 38; 39; 40]. As summarized earlier [34; 35; 40; 41], more specific CFA parameters may provide in-depth understanding of chilling-related physiologically regulated and non-regulated changes in the partition of absorbed radiation energy among various photochemical processes (actual photochemical efficiency of PSII, \(\Phi_{\rm PSII}\); photochemical quenching, \(q_{\rm P}\) and \(q_{\rm L}\)[35] and relevant protection mechanisms (quantum yield of regulated and non-regulated non-photochemical energy dissipation in PSII, \(Y_{\rm NPQ}\), and YNO, non-photochemical quenching, \(q_{\rm N}\) and NPQ [40]). In addition, the detailed evaluation of the polyphasic fluorescence rise [42; 43] of the rapid Kautsky kinetics [44] in the OJIP test [45; 46] may give additional insight into primary photophysical and photochemical events in PSII [46; 47] and can be applied for the rapid evaluation of biotic and abiotic stress effects on the quantum efficiency of PSII photochemistry and the activity of the photosynthetic electron transport chain [48]. Furthermore, non-invasive visible- (VIS-) and near-infrared (NIR) spectroscopy may also reveal important CI-related short- and long-term changes in the contents of relevant photosynthetic (chlorophylls, carotenoids) and non-photosynthetic phenolic pigments [49; 50]. For this purpose, both advanced statistical analyses but also classical parameters such as the normalized difference vegetation index (NDVI), the photochemical reflectance index (PRI), and the normalized anthocyanin index (NAI) are useful tools to analyze spectra obtained [51; 52; 53; 54]. In contrast to CFA [11; 12], VIS remission spectroscopy has not yet been applied for the analyses of CI effects in bananas. Thus, continuous and modulated CFA and imaging, and VIS-spectroscopy were, for the first time, applied concomitantly to rapidly, noninvasively, and comprehensively monitor the effects of a range of relevant low, nonfreezing temperatures (5 \({}^{\circ}\)C, 10 \({}^{\circ}\)C, 11.5 \({}^{\circ}\)C and 13 \({}^{\circ}\)C as control) on various aspects of photosynthetic activity and contents of photosynthetic, photoprotective, and attractive pigments in green-ripe banana fruit. These data provided detailed analyses of the potential dynamics of chilling injury-related variations in photosynthetic activity and photoproduction to better understand these physiological changes during CI development in green-ripe banana.