Acorn Use for Food, Harvesting and Nutrition

Guest Post by David A. Bainbridge 

ACORN HARVESTING

            Harvesting acorns should be very similar to the harvesting of other commercial nuts such as almonds or filberts. Wolf (1945) found that it was possible to collect from 110-660 kg (50-300 lbs) of acorns per hour with very simple hand tools. My own experience has confirmed these numbers. However, when harvesting small acorns, like Q. gambelii, in an off year it may be possible to collect only a few pounds per hour.

ACORN NUTRITION

            The nutritional qualities of 18 species of acorns are described in Table 1. California's acorns are described in Table 2.

TABLE 1.  ACORN COMPOSITION, 18 SPECIES

                                                 Percent          

Water                                          8.7 - 44.6

Protein                                         2.3 - 8.6

Fat                                               1.1 - 31.3

Carbohydrate*                          32.7 - 89.7

Tannin                                         0.1 - 8.8

KCAL/100 gms                         265 - 577

KCAL/lb                                  1200 - 2600

* or N free extract

(Bainbridge, 1985a).

TABLE 2. CALIFORNIA ACORNS

Species              Water        Protein               Fat      Carbohydrate    Tannin

Q.agrifolia1         9.0              6.26                 16.75         54.57            --

Q.chrysolepis¹    9.0              4.13                 8.65           63.52            --

Q.douglasii¹       9.0              5.48                 8.09           65.50               --

Q. douglasii²     40.75            3.03                 4.77           43.39            3.61

Q. dumosa²       44.58           2.29                 3.42           40.65           5.15

Q. kellogii¹          9.0              4.56                17.97        55.48            --

Q. kellogii²        37.6              3.43                11.05        32.71            1.81

Q. garryanna¹      9.0              3.94                 4.47           68.87            --

Q. lobata¹            9.0              4.90                 5.54           69.02            --

Q. lobata²          40.57            2.82                 4.25           43.44            3.85

Q. wislizneii²     29.80            3.08                 14.47         40.40            4.60

Lithocarpus

   densiflora³      36.00            2.06                 8.50           38.29            --

Indian corn⁴      12.5              9.2                   1.9             74.4              --

Wheat⁴              11.5              11.40               1.00           75.4              --

¹Wolf (1945), ²Wagnon(1945), ³Heizer and Elsasser (1980), ⁴Wagnon (1946)

            X-ray diffraction showed that the structure of acorn starch from Q. mongolica and Q. crispula fell between that of corn and potatoes. Acorn starch had limited gelatinization at 61-68oC, with gelatinization of Q. crispula lowest and Q. mongolica highest (Kim and Lee, 1976). The amylose content of acorn starch was 27.1 percent, blue value 0.43 and Aldehyde number 1103 (Chung et al., 1975). Acorns are also good sources of some vitamins, with 5 - 54.8 mg of Vitamin C per 100 gm of raw acorn (Djordjevic, 1954; Minieri, 1954). This compares favorably with the Negev lemon, with 58.1 mg per 100 g. Acorns are also an excellent source of Vitamin A, with 180 IU per gm in Q. phellos (King and Titus, 1943). Twenty-seven grams, or less than tenth of pound of acorns, would meet the suggested daily requirement of 5,000 IU for vitamin A. This may prove of great benefit in areas of the world where vitamin A deficiency is common among the poor. Thorough testing of a full range of oak species and oak processing methods may well discover other species with even higher levels of these and other vitamins and trace elements.

            Acorns include many essential amino acids, Table 3. (Luk'yanets, 1978; Videl and Varela, 1969). Testing is needed to establish the amino acid content of the California species. Minor deficiencies can probably be rectified with complementary legumes, fish, or meats. When acorns are cooked with ash, to neutralize bitterness, the acorn foods should also be a good source of calcium. Cooking with ash may also make more niacin available if the tests Ruttle (1976), conducted on corn are replicable for acorns. Acorns also supply many trace elements. It is not at all surprising that acorn-based cultures prospered for thousands of years with this excellent food base.

TABLE 3: AMINO ACID CONTENT OF ACORNS

                                    milligrams/gram

Glycine                        0.98 - 1.37

Alanine                        1.02 - 1.57

Valine                          0.97 - 1.22

Leucine                       1.69 - 2.08

Isoleucine                    0.63 - 0.72

Serine                          0.94 - 1.23

Threonine                    0.87 - 1.13

Methionine                  0.26 - 0.31

Phenylalanine              0.90 - 1.09

Tyrosine                      0.68 - 0.99

Lysine                         1.19 - 1.51

Arginine                      1.48 - 2.25

Histidine                     0.71 - 1.05

Proline                        1.41 - 1.58

Aspartic acid               2.75 - 3.66

Glutamic acid              3.10 - 4.33

(Luk'yanets, 1978).