Grapes, blue

You can try this yourself at home. You need some purple grape juice, blueberry juice, or the water left over after boiling a red cabbage. If you add clear distilled vinegar, the juice will turn red. If you add baking soda, the juice will turn blue. 

Methods used for the detection of PAs in cmde or partially purified extracts can also be adapted for post-column analysis after fractionation (see below). Direct quantitative analysis of PAs in crude grape phenolic extracts is often impossible due to the complex sample matrix. Thus, fractionation or purification is often necessary before analysis. The Folin-Ciocalteu and Pmssian Blue assays are widely used for the quantification of total polyphenols in plants [27,28]. These methods are not specific for PAs due to the reaction of other phenolic compounds with these reagents. 

CuSiFg, 4H20 mw 277.72 blue, hygroscopic, poisonous crysts sp gr 2.158, mp — decompd sol in w, si sol in ale. Can be prepd by interaction of Cu hydroxide and hydrofluosilicic acid. Used for creating grape vines for "white disease" and for dyeing and hardening white maible (Ref 1)... 

C8H9NO2, Mr 151.16, bp2w 135.5 °C, df 1.1682, ng 1.5815, occurs in a large number of blossom essential oils (e.g., neroli, ylang-ylang, and jasmin oils), grapes, and citrus oils. It occurs as white crystals mp 24-25 °C), or a yellowish liquid, that show blue fluorescence and have an orange blossom odor. Methyl anthranilate is prepared by esterification of anthranilic acid with methanol or by reaction of isatoic anhydride with methanol [163]. 

A welcome side effect of treating fungi (e.g. peronospora plasmopara viticola) with iron blue is the fertilizing of vines in soils that give rise to chlorosis. Leaf color is intensified, ageing of the leaves is retarded, and wood quality ( ripeness ) is also improved [3.196]—[3.198]. Iron is necessary for chlorophyll synthesis, which improves grape quality and yield. Other iron salts do not have this effect [3.197]. 

Red cabbage as a colorant source has been studied for many years. As of 1990 at least one firm has introduced San Red RC, the first commercially available food color derived from red cabbage. The color can be used alone or in combination with other colors to create strawberry, cherry, raspberry, and blueberry tones. By way of proprietary technology, the new dye is claimed to be free of flavor and odor defects, which in the past have been associated with red cabbage. The dye is pH dependent. The color tones move toward blue-red as the pH value increases. San Red RC ranks between cochineal and grape juice in percent or color retention. 

Exempt colors do not have to undergo formal FDA certification requirements, hut are monitored for purity. The colorants exempt from FD C certification are annatto extract, /i-carolene, beet powder, 0-apo—8 -carntenol. canlhaxanthin. caramel, carmine, carrot oil. cochineal extract, cottonseed Hour, ferrous gluconate, fruit juices, grape skin extract, paprika, paprika oleoresin. riboflavin, saffron, titanium dioxide, turmeric, turmeric oleoresin. ultramarine blue, and vegetable juices. See also Colorants (Foods). 

Anthocyanine Red or blue depending on pH Reduced flavonoid Sambucin Elder Sambucus sp.) Blackberries, dewberries (JRubus sp. L.) Grapes (Vitis sp.) Cherries (Prunus sp. L.) ... 

Anthocyanins Grape skins, elderberry, Red-purple-blue, E163 Good Good... 

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