GC-O, volatile and qualitative differences in locally grown rabbiteye and southern highbush blueberries, and juices

Authors: Beaulieu, John; Tully, Maureen; Shaw, Donna; Lloyd, Steven; Grimm, Casey

Submitted to: American Society of Horticulture Science Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 5/11/2018
Publication Date: 8/3/2018
Citation: Beaulieu, J.C., Tully, M.A., Shaw, D.A., Lloyd, S.W., Grimm, C.C. 2018. GC-O, volatile and qualitative differences in locally grown rabbiteye and southern highbush blueberries, and juices. American Society of Horticulture Science Meeting. 236-237.

Interpretive Summary: Southern and southeastern US production of blueberries has increased markedly in recent years. Blueberries are a well-known and documented source of several compounds that have been associated with positive health-promoting benefits. Yet, gas chromatography-olfactometry (GC-O) and volatile compounds are seldom reported in rabbiteye blueberry (RAB). Few comparisons have been made between the organoleptic differences between RAB and southern highbush (SHB) fruits and pressed juices therefrom. Subsequently, a GC-O, GC-MS (mass spectrometry) volatile and physiological quality appraisals in six varieties of SHB and RAB harvested twice in a single season was accomplished. As a means to indicate the significant aspects regarding possible difference in quality attributes, we compared our previously reported pH, Brix and TA values attained by muslin pressing intact previously frozen and thawed fruit to the same samples when used fresh (no freezing) after hand-pressing through nylon in a small stainless steel (Ferrari) press versus after forming an enzyme-digested heated mash followed by hydraulic pressing (nylon sack) with either ultrafiltration or no filtration and pasteurization. Three varieties of RAB (‘Alapaha’, ‘Columbus’ and ‘Montgomery’) and SHB (‘Biloxi’, ‘Magnolia’ and ‘Misty’) blueberries were hand harvested fully ripe, 10 days apart in Poplarville, MS. Samples were assessed for rapid qualitative differences (pH, brix, titratable acidity, color). SPME carboxen/DVB/PDMS fiber absorption on a fully automated Gerstel MPS2 was followed by splitting the run into an Agilent 7890-A GC with flame ionizing detector (FID) with a BreckBühler Sniffer 9000 GC-O port. Volatiles were confirmed separately via identical runs on an Agilent 6890/5973 GC-MS. Freshly pressed berry juice had higher L*, a*, b* and C* but lower hue angles than juices prepared from frozen berries, and similar values compared to pasteurized samples. On the other hand the freshly pressed juices had markedly lower titratable acidity and conversely higher soluble solid to acid ratios compared with frozen pressed samples. Volatiles such as (Z)-3-hexen-1-ol, (E)-geraniol, linalool, linalool oxide, eugenol and ß-damescenone were identified and assessed, and compared against sample aromas and known standard compounds. ‘Alapaha’ contained potent aromas of alcohol, chocolate, blueberry, grass, sweet, fruity, floral, and spice. ‘Montgomery’ had aromas of blueberry, chocolate, fruit, cinnamon, coffee, and alcohol. ‘Magnolia’ was very fragrant, perfume-like juice. The other varieties did not exhibit such potent and distinct odors but, had faint blueberry, sweet, coffee beans, fruity, floral, heated plastic and iron notes. Specific compounds such as (E)-geranyl acetone, linalool oxide, ß-pinene and camphene had matching GC-O, RT and MS confirmations, and these are compounds that are important or possibly important in fruit aroma (e.g. blueberry, sweet, green flower, fruity and floral notes). Berry and juice differences along with volatile and aroma nuances and findings will be explored further.

Technical Abstract: Southern and southeastern US production of blueberries has increased markedly in recent years. Gas chromatography-olfactometry (GC-O) and volatile and semi-volatile compounds are seldom reported in rabbiteye blueberry (RAB). Few comparisons have been made between the organoleptic differences between RAB and southern highbush (SHB) fruits and pressed juices therefrom. We performed GC-O, GC-MS, volatile and physiological quality appraisals in six varieties of SHB and RAB harvested twice in a single season. Three varieties of RAB (‘Alapaha’, ‘Columbus’ and ‘Montgomery’) and SHB (‘Biloxi’, ‘Magnolia’ and ‘Misty’) blueberries were hand harvested fully ripe, 10 days apart in Poplarville, MS. Fruit were either sampled fresh after hydraulic pressing in a small Ferrari press with nylon-mesh to mimic steps toward making a mash and juices, or frozen immediately after harvest, and pressed after thawing via muslin cloth. Commercially frozen RAB (‘Tifblue’) heated mash was enzyme-treated, hydraulically pressed, not filtered and ultrafiltered, and pasteurized juices prepared in our pilot plant for a comparison. Samples were assessed for rapid qualitative differences (pH, brix, titratable acidity, color). SPME carboxen/DVB/PDMS fiber absorption on a fully automated Gerstel MPS2 was followed by splitting the run into an Agilent 7890-A Gas Chromatography (GC) FID with a BreckBühler Sniffer 9000 GC-O (Olfactometer). Volatiles were confirmed separately via identical runs on an Agilent 6890/5973 GC-MS. Freshly pressed berry juice had higher L*, a*, b* and C* but lower hue angles than juices prepared from frozen berries, and similar values compared to pasteurized samples. On the other hand the freshly pressed juices had markedly lower titratable acidity and conversely higher soluble solid:acid ratios compared with frozen pressed samples. Volatiles such as (Z)-3-hexen-1-ol, (E)-geraniol, linalool, linalool oxide, eugenol and ß-damescenone were identified and assessed, and compared against sample aromas and known standard compounds. ‘Alapaha’ contained potent aromas of alcohol, chocolate, blueberry, grass, sweet, fruity, floral, and spice. ‘Montgomery’ had aromas of blueberry, chocolate, fruit, cinnamon, coffee, and alcohol. ‘Magnolia’ was very fragrant, perfume-like juice. The other varieties did not exhibit such potent and distinct odors but, had faint blueberry, sweet, coffee beans, fruity, floral, heated plastic and iron notes. Specific compounds such as (E)-geranyl acetone, linalool oxide, ß-pinene and camphene had matching GC-O, RT and MS confirmations, and these are compounds that are important or possibly important in fruit aroma (e.g. blueberry, sweet, green flower, fruity and floral notes). Berry and juice differences along with volatile and aroma nuances and findings will be explored further.