Here is something I found relating to the degridation of chloraphyl be freezing and also how freezing affect carotenes and anthrocyanin which are all found in cannabis. You'll have to read between the lines abit as this is related to fruit and vegetables.
It may also prove interesting if you also like growing fruits & vegetable like my self and wish to freeze them.
I have copied and pasted the following article from -Handbook of fruits & fruit processing.
Hope you find it interesting, as it shows how freezing vegetation can be adapted as a curing method for cannabis.
Color Changes.
Color is the most important quality characteristic of fruits because it is the first attribute perceived by the consumers and is the basis for judging the product acceptability.
The most important color changes in fruits are related to chemical, biochemical, and physicochemical mechanisms:
(a) breakdown of cellular chloroplasts and chromoplasts,
(b) changes in natural pigments (chlorophylls,
carotenoids, and anthocyanins), and (c) development
of enzymatic browning.
Mechanical damage (ice crystals and volume expansion) caused by the freezing process can disintegrate the fragile membrane of chloroplasts and chromoplasts,
releasing chlorophylls and carotenoids, and facilitating their oxidative or enzymatic degradation.
Also, volume expansion increases the loss of anthocyanins by lixiviation due to disruption of cell vacuoles.
(i) Chlorophylls. Chlorophylls are the green pigment of vegetables and fruits, and their structures are composed of tetrapyrroles with a magnesium ion at their center.
Freezing and frozen storage of green vegetables and fruits cause a green color loss due to degradation of chlorophylls (a and b) and transformation in pheophytins, which transfers a brownish color to the plant product (Cano, 1996).
One example is kiwi-fruit slices that show a decrease in chlorophyll concentration between 40% and 60%, depending on cultivar, after freezing and frozen storage at −20◦C for 300 days (Cano et al., 1993a).
Different mechanisms can cause chlorophyll degradation; loss of Mg due to heat and/or acid, which transforms chlorophylls into pheophytins; or loss of the phytol
group through the action of the enzyme chlorophyllase (EC 3.1.1.14), which transforms chlorophyll into pheophorbide.
Loss of the carbomethoxy group may also occur and pyropheophytin and pyropheophorbide can be formed (Fig. 4.5.) (Heaton et al., 1996).
Acids, temperature, light, oxygen, and enzymes easily destroy the chlorophylls. Thus, blanching (temperature/time), storage (temperature/time), and acidity are the important factors to be controlled during processing in order to preserve chlorophylls.
Other chlorophyll degradation mechanism can cause degradation by the action of peroxides, formed in the fruit tissue due to the oxidation reaction of polyunsaturated fatty acids catalyzed by the enzyme LOX.
An important quality parameter employed to determine the shelf life of frozen green fruits is the formation of pheophytins from chlorophylls. As different types of enzymes can be involved in chlorophyll degradation (LOX, POD, and chlorophyllase), blanching and addition of inorganic salts such as sodium or potassium chloride and sodium or potassium sulphate are efficient treatments to preserve green color (IIR, 1986; Cano and Mar�ın, 1992; Cano et al., 1993a, b).
(ii) Carotenoids. Carotenoids are among the most abundant pigment in plant products and are responsible for the yellow, orange, and red color of most of
the fruits. All of them are tetraterpenes and contain 40
carbon atoms in eight isoprenes residues. -carotene and lutein are the carotenoids present in most of the fruits. Important sources of these pigments are as follows (Figure 4.6): -cryptoxanthin: oranges lycopene: tomatoes, watermelon, papaya and persimmon -carotene: banana and avocado zeaxanthin: orange and peach Carotenoids are affected by pH, enzymatic activity, light, and oxidation associated with the conjugated double bond system. The chemical changes occurring in carotenoids during processing have been reviewed by several authors (Simpson, 1986; Rodriguez-Amaya, 1997). The main degradation reaction that damages carotenoid compounds is isomerization.
Most plants appear to produce mainly transforms of carotenoids but with increased temperature, the presence of light, and catalysts such as acids, isomerization to the cis forms increases, and the biological activity is dramatically reduced.
However, heat treatments of products rich in carotenoids reduce the degradation of carotenoids because of the inactivation of enzymes LOX and POD. Blanching fruits before freezing could be efficient in the preservation of carotenoids due to enzyme inactivation.
Although most carotenoids are heat resistant, some carotenoids, such as epoxycarotenoids, could be affected. Carotenoids are fat-soluble pigments and
breakdown of chromoplasts, by heat treatment or mechanical damage, improves their extraction with organic solvents and bioavailability but not their loss by lixiviation (Hof et al., 2000).
Freezing without protector pretreatment slightly decreases total carotenoid concentration (20%) of some fruits rich in carotenoids, such as mango and papaya. But after 12 months of frozen storage at −18◦C, an important decrease of total carotenoid concentration (between 40%and 65%) occurred, although the carotenoid profilewas unchanged (Cano and De Ancos, 1994; Cano et al., 1996b). Similar results have been found with frozen tomato cubes. A pronounced stability of total carotenoids, -carotene, and lycopene was recorded up to the 3rd month of storage. But after 12 months of storage at −20◦C, the losses of carotenoids reached 36%, of -carotene 51%, and of lycopene 48% (Lisiewska and Kmiecik, 2000). Freezing and frozen storage could affect the carotenoid structure and concentration depending on the type of fruit and cultivar (pH, fats, antioxidants, etc.) and the processing conditions (temperature, time, light, oxygen, etc.)
(Simpson, 1986; Rodriguez-Amaya, 1997). (iii) Anthocyanins. Anthocyanins are one class of flavonoid compounds, which are widely distributed plant polyphenols, and are responsible for the pink, red, purple, or blue hue of a great number of fruits (grape, plum, strawberry, raspberry,
blackberry, cherry, and other types of berries).They are water-soluble flavonoid derivatives, which can be glycosylated and acylated. The effect of freezing, frozen storage, and thawing in different fruits rich in anthocyanins pigments have been reviewed by Skrede (1996). Anthocyanins in cherry fruit underwent pronounced degradation during storage at −23◦C (87% after 6 months), but they are relatively stable at −70◦C storage (Chaovanalikt and Wrolstad, 2004). But in raspberry fruit, the stability of anthocyanins to freezing and frozen storage depends on the seasonal period of harvest. Spring cultivars were practically unaffected by freezing and frozen storage for 1 year at −20◦C, but autumn
cultivars showed a decreasing trend in total anthocyanin content (4�17%)(De Ancos et al., 2000b). In general, the freezing process does not affect the level of anthocyanins in raspberry fruit (De Ancos, 2000; Mullen et al., 2002). Authors explain degradation of anthocyanins during frozen storage by different chemical or biochemical mechanisms. Anthocyanins are water-soluble pigments located in the vacuoles of cell and are easily lost by lixiviation when the cell membranes break down. Also oxidation can play an important role in anthocyanin degradation
catalyzed by light. PPO and POD enzymatic activities have been related to anthocyanin degradation. Thus, frozen�thawed cherry discoloration disappeared
when the fruits were blanched before freezing.The changes in pH during processing can affect anthocyanin stability. Maintenance of red fruit requires
an acid medium (pH < 3.5). The flavylium cation structure of anthocyanins transfers a red color to the fruit. But an increase in pH value produces a change
from red to blue until the product is colorless, a consequence of transforming flavylium cation into a neutral structure (Fig. 4.7). The loss of characteristic red color can also be produced by formation of the anthocyanin complex with
different products present in the fruit matrix: ascorbic acid, acetaldehyde, proteins, leucoanthocyanins, phenols, quinones, metals (Fe3+ and Al3+), hydrogen peroxide, etc. (Escribano-Bailon et al., 1996).(iv) Enzymatic Browning. Browning usually occurs in certain fruits during handling, processing, and
storage. Browning in fruit is caused by enzymatic oxidation of phenolic compounds by PPO(EC 1.10. 3.1) (Mart�ınez-Whitaker, 1995).
PPO catalyzes either one or two reactions involving molecular oxygen. The
first type of reaction is hydroxylation of monophenols, leading to formation of o-hydroxy compounds.
The second type of reaction is oxidation of o-hydroxy compounds to quinones that are transformed intopolymeric brown pigment (Fig. 4.3). Freezing, frozen
storage, and thawing of fruits, like mangoes, peaches,bananas, apples, apricots, etc., quickly develop color changes that result in nonreversible browning or
darkening of the tissues. Freezing does not inactivate enzymes; however, some enzyme activity is slowed during frozen storage (Cano et al., 1998). Browning
by PPO can be prevented by the addition of sulfites, ascorbic acid, citric acid, cysteine, and others. The addition of antibrowning agents has been discussed in
the pretreatments section. Selection of varieties with low PPO activity could help to control browning infrozen�thawed fruits (Cano et al., 1996b; Cano et al.,
1998
Peace
Growerz