All About Almonds: Effect of Processing on Energy, Macro-, Micro- & Phytonutrient Content, Quality + (Bio-)Availability

I guess you won't be surprised to hear about advantages of raw almonds, but what about the skin...?

In view of the repeatedly resurfacing hype around almonds, I probably don't have to tell you that the oval nutlike seed (kernel) of the almond tree, which grows in a woody shell is another of the infamous superfoods. Now, this alone wouldn't be reason enough for almonds to make it into the SuppVersity News, again (!); rather than hype, it's their phytochemicals and nutrient content of which several lines of experimental and epidemiological research suggest that they have positive health benefits in relation to heart disease, diabetes and obesity.

What should be obvious, though, is that these benefits will be observed only if these precious phyto- and micronutrients are (a) retained upon processing / mastication and (b) digested and absorbed during the digestion process.
As Myriam Marie-Louise Grundy and colleagues from the King’s College London and the almond pimp organization in California, i.e. the "Almond Board of California" (this doesn't make the paper worthless, but, as usual, we have to review the conclusions critically) point out in a recently published review, "[r]ecent studies have demonstrated the importance of food structure during the digestion of plant foods" (Grundy. 2016).

The food structure? Yeah. What the scientists refer to are differences as you will observe them between raw whole, roasted, skinned or deskinned almonds or almonds vs. almond butter. In other words we are not talking about food combining, the far reaching effects of which I have discussed in previous articles, but rather about the way/s and degree/s of processing and how this may affect the previously hinted at health benefits of almonds.

Figure 1: Multiscale structure of almond fruit with kernel. Note that the size of the almond cell is about 35 lm and the oil body between 1 and 5 µm (Grundy. 2016).

Structure-wise almonds have a certain similarity to plums, cherrie, or olives. All of them belong to the genus of stone foods which have a thin skin and a central stone that contains the seed (Gradziel. 2011), which, is where - at least in the case of almonds - the actual, or I should say alleged (?) nutritional magic (Figure 1).

Table 1: Nutrient and total phenolic composition of almonds (Grundy. 2016)

What paleo fanatics will know is that almonds' major storage protein (70%) found in almonds is amandin or 'almond major protein', a protein that belongs to the class of legumins - albeit one of which you will have a hard time to find convincing scientific evidence that its purported anti-nutrient effects are worth worrying about.

Apropos, the overview of macro- and micronutrients in 100g of almonds in Table 1 on the right tells you that they are an excellent source of magnesium and phosphorus, a good source of calcium and a decent source of copper and zinc (the ratio is yet a bit off towards the copper side of things) and almost enough manganese (RDA 2.2 mg for men, 1.8 mg for women) - an often-overlooked micromineral that plays a vitally important role in our carbohydrate, amino acid, and cholesterol metabolism and the control & maintenance of our antioxidant defenses (Finley. 1999).
Ah, and of course, there are the polyphenols, mainly proanthocyanidins, flavonoids and phenolic acids, which are held responsible for much of their anti-oxidant and corresponding downstream effects, and phytosterols (mostly  b-sitosterol), which have been linked to their anti-cholesterol (LDL) and pro heart health effect. In that, it is interesting to note that the former, i.e. polyphenols, can mostly be found in the skin, while the latter, i.e. phytosterols that come in dosages of ~270mg (cf. Table 1) can be found in highest concentrations in the kernels. One effect of processing should thus be clear: removing the skin is going to significantly (almost completely) reduce the amount of polyphenols you can derive from almonds. So, let's take a look at the other effects that occur upon almond processing and during the production of marzipan as well as almond butter, milk and oil:

• Roasting - With hot air and oil roasting, with variations in heating times and duration to obtain light, medium or dark roasts, roasting is one of the most frequently used processing techniques in almonds. That this puts the relatively high concentration of PUFAs in harms way should be obvious.
  
  The good news, however, is that an extensive oxidation of PUFAs would increase off-flavours and are thus relatively high on the manufacturers "need to be prevented" list. That's in contrast to the maillard reactions which are reactions between reducing sugars and amino acids and eventually the reason why roasted almonds brown and taste differently.
  

  Table 2: Effect of roasting on almond structure and composition (Grundy. 2016).

  The first non-visible change to almonds is a significant increase in energy content with roasting that is a mere result of the 40-60% loss of non-caloric water-weight from the nuts.
  
  As Grundy et al. point out, this is unfortunately, not the only potentially ill effect of roasting, which will affect the proteins (could be benficial for the legume haters) and also destroy the oil bodies and the endoplasmic network - a process that can "greatly affect thestructure of almond cells, the cell walls as well as the intra-cellular oil bodies" (ibid.). Ideally without significantly oxidizing the oil potion, but inevitable coalesce to form larger oil droplets than the ones observed in raw almond cells - an effect that could increase the uptake of the lipids by 7.2-10.3 % (Altan. 2011).
  

  Figure 2: Photographs of the almond samples fractured after compressing in the texture analyser, examples of (left) raw and (right) 6-min roasted (Varela. 2006).

  The benefits of roasting are mostly culinary ones. The formation of Maillard products, reduction of moisture and related effects give roasted almonds a slightly different taste and make them more brittle & crunchy and produced more loose particles postchewing than whole raw almonds (Varela. 2006).
• Particle size reduction aka crushing the almonds - We often overlook how chewing (aka mastication) and other forms of "particle size reductions", including far-reaching interventions such as turning almonds into almond butter, can have on the energy, macro-, micro- and phytonutrient content, quality and (bio-)availability of our foods.
  
  Whole natural, blanched and roasted almond can be further processed to obtain almond particles of different shape and size (Fig. 3). The list of possible processing steps include slicing, dicing, chipping, grounding and slivering (Wareing. 2000)
  

  Figure 3: Change in  hunger (A) and fullness (B) after ingestion of 55 g almonds w/ every meal for 4 days. The almonds were chewed 10-, 25- and 40-times before swallowing (Cassaday. 2009) and photographs of ground almond particles with different size ranges (Grundy. 2016 | added ex-post to the graphs from Cassaday. 2009).

  As Grundy et al. (2016) point out with reference to previous studies (Grundy. 2015), the corresponding almond products differ in the proportion of intact and ruptured cells and thus the nutrient availability upon digestion, hunger and fullness and the energy and nutrient loss in the feces, which is sign. higher if the almonds were neither pre-processed nor properly (>10 times) chewed (see Figure 3 | lipid excretion: 10 chews 43.7% +/- 4.0%; 25 chews 32.7% +/- 2.7%; 40 chews 30.8% +/- 4.4% | maximal energy loss: ~910 kcal / 4 days in 10 chews; ~780 kcal / 4 days in the 25 chews group and ~740 kcal / 4 days in the 40 chews group).
  
  

  Table 3: Nutritional property of nut and seed butter (serving size: 1 Tbsp = 14.19 g | table from Gorrepati. 2015)

  In that, smaller particles have more fractured cells and thereby greater nutrient release (bioaccessibility) than larger particles. Practically speaking this means that almond paste, or marzipan are going to make the remaining nutrients more, while raw unprocessed almonts (worst of all badly chewed) will make them less available to our digestive tract. One thing you should not forget, though, is that many of these processed foods contain extra-ingredients. Almond butter, just like any other "nut butter", must >= 90% nut compounds as particles (chunk and/or flour), paste, oil or a combination (Wilkes. 2012; Gorrepati. 2015).
  
  An aspect that has gotten the scientists attention only more recently (Taylor. 2016) are the differential effects of whole raw (=pasteurized - that's necessary by law in the US) almonds, roasted almonds, chopped almonds, and almond butter of which Taylor et al. report that a "[c]omparisons between control and each of the four almond treatments revealed that chopped almonds increased the relative abundances of Oscillospira (p=0.02), Roseburia (p=0.02), and Lachnospira (p=0.04)," low levels of which have - among other pathologies - been linked to obesity, reduced butyrate production and the absence of the previously discussed benefits of SCFA on metabolism and immune health, asthma in children, respectively - if that's what you are aiming for dice / chop your almonds before eating them.
• Blanching, homogenization (for milk) and oil extraction - Compared to roasting, blanching and oil extraction are almost "exotic" means of almond processing with far-reaching effects on the almond tissue / cellularity (see overview in Table 3).
  

  Table 4: Effect of blanching and oil extraction on almond structure and composition (Grundy. 2016)

  If you don't roast almonds and thus kill almost all potentially existing bacteria and fungi, you got to do something else to get rid of bacteria and mold. The easiest (and most obvious way) to do that is to remove the almonds' skin by either wet or dry methods.
  

  Table 5: No sign decrease in antigenicity (=allergy risk) w/ industrial blanching (Venkatachalam. 2002).

  During this process, both, the previously discussed removal of the majority of flavonoids and other phenolic compounds, which confer the skin’s antioxidant properties and are most concentrated in the skin, as well as the exposure to sterilizing heat (85-100°C) can induce sign. changes to the cytoplasmic organization without affecting the protein structure and thus the allergic potential of almonds, significantly (Venkatachalam. 2002).
  

  Table 6: Summary of processing effects on almonds  (Vanga. 2016).

  Interestingly, there's no good evidence on the efficacy of longterm soaking alone, which is applied often-times to produce he "skinned" control in studies. Whether the highly popular soaking alone actually works is thus, as Vanga et al. (2016) point out, uncertain even with sign. longer soaking times (12h+) and the use of lemon water (pH 3.2 - 3.2) and sodium chloride (1.6% w/v) to help solve the skin and maybe also to increase the amount of "allergens that [are being transferred] to water or solution during soaking" (Vanga. 2016).
  
  Another almond product that is commonly treated with pressure and heat is commercially available almond milk. A product that exposes, as a consequences, reduced lipid particles / droplet sizes, a modified rheology and protein structure and - you guessed it - a sign. reduce d allergenic potential of almond proteins (Dhakal. 2014). Since heating alone disrupts the monolayer of phospholipids and proteins is dis rupted during the subsequent heat treatment, it takes the homogenization process to affect the lipid structure (i.e. remove the large fluffy lipids - just as its done in cow's milk and probably with similar potential health risks). With almond oil gaining some popularity, you should lastly know that the cheaper oils are probably produced by chemical extraction techniques, because they produce a much higher yield - at the expense of the quality of the oil, obviously (a loss of purity and reduction of the micronutrient content) compared to cold-pressed oil, which has a light and pale amber colour and, who guessed (otherwise it wouldn't be an oil), a complete loss of integrity in the oil bodies completely lose their integrity. Oxidation, on the other hand, is less of an issue as "the vitamin E and phenolic compounds contained in the oil inhibit its oxidation" (Grundy. 2016).

References:

• Cassady, Bridget A., et al. "Mastication of almonds: effects of lipid bioaccessibility, appetite, and hormone response." The American journal of clinical nutrition 89.3 (2009): 794-800.
• Dhakal, Santosh, et al. "Effect of high pressure processing on the immunoreactivity of almond milk." Food research international 62 (2014): 215-222.
• Finley, John Weldon, and Cindy D. Davis. "Manganese deficiency and toxicity: are high or low dietary amounts of manganese cause for concern?." Biofactors 10.1 (1999): 15-24.
• Gorrepati, Kalyani, S. Balasubramanian, and Pitam Chandra. "Plant based butters." Journal of food science and technology 52.7 (2015): 3965-3976.
• Gradziel, Thomas M. "Origin and dissemination of almond." Horti Rev 38 (2011): 23-81.
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• Grundy, Myriam Marie‐Louise, Karen Lapsley, and Peter Rory Ellis. "A review of the impact of processing on nutrient bioaccessibility and digestion of almonds." International Journal of Food Science & Technology (2016).
• Lee, Jihyun, et al. "Quantification of amygdalin in nonbitter, semibitter, and bitter almonds (Prunus dulcis) by UHPLC-(ESI) QqQ MS/MS." Journal of agricultural and food chemistry 61.32 (2013): 7754-7759.
• Natoli, Sharon, and Penelope McCoy. "A review of the evidence: nuts and body weight." Asia Pacific journal of clinical nutrition 16.4 (2007): 588-597.
• Taylor, Andrew M., et al. "Impact of Almond Consumption on the Composition of the Gastrointestinal Microbiota of Healthy Adult Men and Women." The FASEB Journal 30.1 Supplement (2016): 406-5.
• Vanga, Sai Kranthi, and Vijaya Raghavan. "Processing Efects On Tree Nut Allergens: A Review." Critical reviews in food science and nutrition just-accepted (2016): 00-00.
• Varela, P., et al. "Crispness assessment of roasted almonds by an integrated approach to texture description: Texture, acoustics, sensory and structure." Journal of chemometrics 20.6‐7 (2006): 311-320.
• Venkatachalam, M., et al. "Effects of roasting, blanching, autoclaving, and microwave heating on antigenicity of almond (Prunus dulcis L.) proteins." Journal of agricultural and food chemistry 50.12 (2002): 3544-3548.
• Wareing, P. W., L. Nicolaides, and D. R. Twiddy. "Nuts and nut products." The microbiological safety and quality of food 1 (2000): 919-940.
• Wilkes, Richard S. "Nut butter and related products enriched with omega-3." U.S. Patent Application No. 13/380,279.