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| Carrots and blueberries - superfoods you cannot ruin by grinding, blending and even the falsely depreciated use of the microwave oven. |
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| The scientists didn't just assess the content of vitamins and phenols, but also tested the free radical scavenging and absorbing capacity, as well as the biological, anti-inflammatory effects of the processed blueberries and carrots. |
"Carrots were cut into one-inch length, accurately weighted and blended with pure water (1:2, w/v) for 20 s using the highest speed in a blender. The blended samples were separated into two parts, one part was microwaved for 10 s to inactivate the enzymes in the carrots or blueberries, while another part was not microwaved to examine whether and how their inherent enzymes might alter the releasable level of bioactive components. The blended carrot samples were centrifuged at 10,000 g for 5 min, and the supernatant was collected and the calculated volume of acetone was added to make a final concentration of 50% acetone (v/v) for further assays. Blueberries were extracted following the same procedure without cutting. The extracts were kept at 4°C until testing" (Gao 2017).
Afterward, the samples were analyzed for their free radical scavenging ability using DPPH, ORAC, hydroxyl radical (HOSC) and - most importantly - macrophage cell assays (the latter mirror the biological effects of the extracts much better than the aforementioned chemical assays) - and here's what they found:
- The β-carotene availability in carrots concentration extracted from the chopped carrot was below the limit of detection (LOD). All tested commercial blenders were able to enhance the release of β-carotene at a level of 0.2–0.94 μg/g fresh carrot, which was significantly greater than the chopped counterpart.
There was no significant difference in extractable concentration of β-carotene among the blended/ground carrots using different commercial blenders, regardless of microwaving immediately after grinding.![]()
Figure 1: HPLC analysis of β-carotene in carrot extracts. The results are reported in μg β-carotene per gram of fresh carrot. The vertical bars represent the standard deviation (n = 3) of each data point. Bar with different letter represents significant different at p < .05. HPLC (Gao 2017)
In addition, no difference in extractable β-carotene was observed between the ground carrots using the same blender with and without microwaving. - The anthocyanin content of the blueberry samples was not affected by any of the preparation methods. If you scrutinize the data in Figure 2 you will see that the differences in anthocyanin content for all samples were well within the statistical margin or error for the HPLC analysis for all commercial blenders/grinders.
Microwaving, on the other hand, did change the content of these powerful antioxidants [(a) malvidin-3-O-glucoside and (b) cyanidin- 3-O-glucoside were measured representative for the total anthocyanin content] - and significantly that is. The scientists argue that this difference may be explained by a decrease in the activity of inherent enzymes such as glucosidases and other carbohydrases. Unfortunately, these enzymes have previously been shown to increase the bioactive availability from fruits and other botanicals including vegetables (Otieno 2007; Alrahmany 2012).
As Gao et al. explain, microwaving your blueberries may thus be a bad idea, even though it increases the extractable level of malvidin-3-O-glucoside and cyanidin-3-O-glucoside, because a reduction of these compounds at the expense of their degradation products could eventually imply a reduced bioavailability, because some of their "degradation products such as malvidin and cyaniding might have greater absorption in GI track" (Gao 2017).![]()
Figure 2: HPLC analysis of (a) malvidin-3-O-glucoside and (b) cyanidin-3-O-glucoside in blueberry extracts. The results are reported in μg anthocyanins per gram of fresh carrot. The vertical bars represent the standard deviation (n = 3) of each data point. Bar with different letter represents significant different at p < .05 (Gao 2017). - The total phenolic content (TPC) of carrots ranged from 0.19 to 0.34 mg gallic acid equivalents per gram of fresh carrot, which was equivalent to 593.6–1062.2 mg chlorogenic acid per kilogram of fresh carrot.
While no difference in extractable TPC was detected in carrot samples processed with different blenders, and the chopped carrots, the total antioxidant prowess (measured by TPC) was increased with blending under the experimental conditions, "suggesting the potential effect of particle size in bioactive release from vegetables" (Gao 2017). In addition, microwaving had no significant effect on the extractable amount of phenolics from ground carrots. In a similar vein, the total phenolic content of the blueberries was observed to increase with grinding, which is obviously similar to chewing (blending had no significant effect).![]()
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In contrast to carrots, however, the availability of total phenolic contents in the blueberries did, however, increase significantly with microwaving, "indicating that inactivation of blueberry enzymes might reduce the loss of phenolics during grinding and storage of the blended blueberries" (Gao 2017), so that the TPC results clearly indicate that "microwaving immediately after blending may be recommended for blended blueberry to retain a desirable availability of total phenolics" (Gao 2017).
The TROLOX radical scavenging, ORAC radical absorbance, and hydroxyl radical scavenging capacity (HOSC) While the DPPH (TROLOX) assay was more or less randomly affected by blending and/or microwaving, the ORAC and HOSC assays showed a statistically significant increase in radical absorbance capacity with blending or grounding. Microwaving, on the other hand, increased only the ORAC, not the HOSC capacity - "a possible effect from the inherent carrot enzymes" (Gao 2017) and thus the release of bioactives.![]()
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For blueberries, all three assays, i.e. the DPPH assay (TROLOX), the ORAC assay and the HOSC assay produced more or less random effects - a clear trend for increased or decreased values with either blending, grinding or microwaving was not observed.- The biological anti-inflammatory activity that was measured in macrophages that were exposed to an LPS challenge, no differences were observed for both, the carrot and blueberry samples prepared using different commercial blenders/grinders in releasable levels of potential anti-inflammatory components in the LPS-induced IL-6 mRNA expression in macrophage cells (Figure 7). The inhibitory effects of blueberry extracts on LPS-induced COX-2 and TNF-α mRNA expressions could be dose-dependent.
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| Frozen blueberries are 'better' than 'fresh' ones unless you gather them yourself (Gustafson 2012). |
So, if you buy frozen blueberries, defrost them in the microwave oven and blend them that's not worse than eating the 'fresh' blueberries from the farmers' market (you cannot tell me that the 'farmer' gathered them in the morning before he sells them). In fact, doing the former may have two important advantages: (a) the frozen blueberries may actually be "fresher" and more nutritious than the ones from the farmers' market (see Figure) so that the small drop in their health promoting effects matters only if supermarket stored the blueberries for years (Skupień. 2006) | Comment!
- Alrahmany, Roaaya, and Apollinaire Tsopmo. "Role of carbohydrases on the release of reducing sugar, total phenolics and on antioxidant properties of oat bran." Food chemistry 132.1 (2012): 413-418.
- Gao, Boyan, et al. "Home‐based preparation approaches altered the availability of health beneficial components from carrot and blueberry." Food Science & Nutrition (2017).
- Gustafson, Sally J., et al. "Effect of postharvest handling practices on phytochemical concentrations and bioactive potential in wild blueberry fruit." Journal of Berry Research 2.4 (2012): 215-227.
- Otieno, D. O., J. F. Ashton, and N. P. Shah. "Isoflavone phytoestrogen degradation in fermented soymilk with selected β-glucosidase producing L. acidophilus strains during storage at different temperatures." International journal of food microbiology 115.1 (2007): 79-88.
- Zaiter, Ali, et al. "Effect of particle size on antioxidant activity and catechin content of green tea powders." Journal of food science and technology 53.4 (2016): 2025-2032.