**3.5. Effect of production systems on phenolic composition**

**3.4. Effect of production systems on antioxidant capacity**

206 Phenolic Compounds - Natural Sources, Importance and Applications

**TPC (μg GAE g−1)**

Production systems

Matted row system

Plastic mulch

Plastic mulch with row covers

micromoles of Fe<sup>2</sup>

(*p* < 0.05).

SO<sup>4</sup> ∙7H<sup>2</sup>

LSD (*p* < 0.05): least significant difference at the 0.05 level.

**TAC (μmol g−1)** **ORAC (μmol TE g−1)**

Production systems significantly changed the TPC, TAC and ORAC, but the effects varied during the different harvests (**Table 4**). PMRC promoted TPC, TAC and ORAC of strawberry fruits compared to MRS throughout the harvest season. At early harvest, TPC, TAC and ORAC were significantly higher for PMRC than MRS, but the differences of TPC and TAC between PM and MRS were not significant (**Table 4**). At mid harvest, TPC, TAC and ORAC reached the peak, and PM showed a significant change of TPC and ORAC compared to MRS. PM showed a significant change of TAC compared to MRS until the late harvest (**Table 4**). The increase of TPC and TAC might be attributed to the changes of microenvironment temperature, moisture, various enzyme activities and rhizospheric microflora of soil under the PMRC compared to the MRS which promoted the growth stages similar to the finding of Wang et al. [19] who reported that fruits from hill plasticulture had higher flavonoid contents and TAC than the MRS. The fruits harvested from PMRC not only showed the higher TPC and TAC but also the better shelf life than those from MRS in our study. The relation between antioxidant activity and fruit shelf life could be explained by our previous research that some of the antioxidants may reduce the incidence of postharvest diseases during storage and be responsible for postharvest quality [34]. Similar results were found by Wang and Millner [35] which indicated that cultural systems affected ORAC values, flavonoids and anthocyanins of 'Allstar' and 'Chandler' strawberries. ORAC is another new method of measuring antioxidant

**Early harvest Mid harvest Late harvest**

**TPC (μg GAE g−1)**

**TAC (μmol g−1)**

1437.9b 14.5b 20.6c 1522.8c 15.0b 22.4c 1355.8b 14.1c 21.5c

1521.1ab 14.7b 22.4b 1698.0b 16.4ab 24.1b 1603.3a 15.5b 22.4b

1610.2a 16.1a 24.3a 1867.4a 17.8a 25.2a 1631.4a 16.8a 23.6a

LSD0.05 155.8 1.2 0.9 140.4 1.5 0.9 168.6 1.0 0.8

O equivalent per gramme of fresh frozen weight.

absorbance capacity (ORAC) of strawberry selection 'SJ8976-1' grown under three production systems.

TPC is expressed as micrograms of gallic acid equivalent (GAE) per gramme of fresh frozen weight; TAC is expressed as

Different lower-case letters in the same column indicate statistically significant differences between different treatments

**Table 4.** Early-, mid- and late-harvest total phenolic content (TPC), total antioxidant capacity (TAC) and oxygen radical

TPC and TAC were performed in triplicate for each of three replicates in 2009 and 2010.

**ORAC (μmol TE g−1)**

**TPC (μg GAE g−1)**

**TAC (μmol g−1)**

**ORAC (μmol TE g−1)**

Phenolic compounds, found in numerous fruits, vegetables and beverages, were not only providing supplemental functions in a plant's life cycle but also offering health benefits to humankind. They have been viewed as potential sources of dietary constituents to prevent the majority of diet-related diseases such as high cholesterol, high blood pressure and obesity. In our study, the main phenolic compounds identified by HPLC analysis in strawberry selection 'SJ8976-1' were grouped into six major categories: anthocyanins, hydroxycinnamic acids, kaempferol, flavonols, ellagic acid and benzoic acids. Among the six categories, anthocyanins accounted for 53.5% of the total phenolics and turned out to be the most predominant phenolic compounds. The physiological function of anthocyanin is responsible for the red colour of the strawberry skin and flesh. The second most abundant category was hydroxycinnamic acids, which accounted for 24.5% of the total phenolics, while kaempferol accounted for only 2.2% which was the lowest percentage of the total phenolics (**Table 5**).

In general, the strawberry fruits harvested from PMRC represented significantly higher amount of total phenolics than those from MRS and PM at all the three harvests based on the sum of the six categories of phenolic compounds (**Table 5**). In detail, significantly higher ellagic acid was assessed in the fruits from PMRC and PM than those from MRS. PMRC significantly enhanced total benzoic acids in strawberry fruit compared to MRS and PM during the early harvest, but the differences were no longer significant at mid and late harvests. Fruits harvested under PMRC showed significantly higher total hydroxycinnamic acids than MRS and PM in early harvest, and from mid to late harvest, the accumulation of hydroxycinnamic acids maximized in a peak. Those fruits from PMRC had no significantly higher amount of flavonols than those from MRS and PM at beginning, but the amount of flavonols grew quickly and achieved the peak by end of mid harvest under all three production systems; at late harvest fruit from PMRC and PM presented significantly higher total flavonols than MRS. Moreover, during all the harvests, significantly higher total anthocyanins accumulated under PMRC than the strawberry from MRS.

The modified phenolic compositions of strawberry under row covers may be primarily attributed to the elevated temperature, transmitted light spectrum and soil acidity inside the covers. Similar findings were observed in tobacco that the interaction of variety and cultural practices had significant effect on total polyphenols, rutin and chlorogenic acid in tobacco leaves [36]. Sharma et al. [37] also informed that mulching itself or combined with row covers had significant influence on plant physiology characteristics and berry yield of strawberry.

The subgroups of anthocyanins and hydroxycinnamic acids detected in strawberry selection 'SJ8976-1' were cyanidin-3-glucoside, pelargonidin-3-glucoside, pelargonidin-3-rutinoside and m-Coumaric acid, o-Coumaric acid and p-Coumaric acid, respectively. m-Coumaric acid, varied from 38.8 to 96.0 μg/g, was the major representative of the hydroxycinnamic acids.


**Table 5.** Early-, mid- and late-harvest phenolic composition (μg g−1 fresh frozen weight) of strawberry selection 'SJ8976-1' grown under three production systems. In contrast, o-Coumaric acid varied from 0.5 to 4.0 μg/g from early to late harvest accounted for the lowest portion of hydroxycinnamic acids. Moreover, the content of p-Coumaric acid, m-Coumaric acid and o-Coumaric acid was significantly promoted by PMRC at all stages (**Table 6**). Pelargonidin-3-glucoside was the dominant anthocyanin measured in strawberry selection 'SJ8976-1', while cyanidin-3-glucoside and pelargonidin-3-rutinoside were found in smaller amounts. PMRC significantly promoted the contents of pelargonidin-3-glucoside and cyanidin-3-glucoside compared to MRC, while the production systems only had the significant effect on pelargonidin-3-rutinoside at the late harvest (**Table 6**).


Anthocyanins were quantified using cyanidin-3-glucoside (C3G), pelargonidin-3-glucoside (P3G) and pelargonidin-3-rutinoside (P3R); hydroxycinnamic acids were quantified using *p*-Coumaric acid (pC), *m*-Coumaric acid (mC) and *o*-Coumaric acid (oC); kaempferol was quantified using kaempferol-3-glucoside (K3G); flavonols were quantified using quercetin-3-galactoside; benzoic acids were quantified using gallic acid, and the authentic standard was used for ellagic acid.

LSD (*p* < 0.05): least significant difference at the 0.05 level.

**Treatment**

Early harvest

Matted row system

Plastic mulch

Plastic mulch with

21.2a

28.7a

68.8a

row cover

LSD0.05 Mid harvest

Matted row system

Plastic mulch

Plastic mulch with

19.6a

24.8a

80.3a

row cover

LSD0.05 Late harvest

Matted row system

Plastic mulch

Plastic mulch with

19.0a

24.2a

108.5a

row cover

LSD0.05 % Total

6.3 quantified using *p*-Coumaric acid (pC),

LSD (*p* < 0.05): least significant difference at the 0.05 level.

8.3

24.5

3.2

3.7

20.6

1.0 2.2 Anthocyanins were quantified using cyanidin-3-glucoside (C3G), pelargonidin-3-glucoside (P3G) and pelargonidin-3-rutinoside (P3R); hydroxycinnamic acids were

quantified using quercetin-3-galactoside; benzoic acids were quantified using gallic acid, and the authentic standard was used for ellagic acid.

Different lower-case letters in the same column indicate statistically significant differences between different treatments (*p* < 0.05).

**Table 5.** Early-, mid- and late-harvest phenolic composition (μg g−1 fresh frozen weight) of strawberry selection 'SJ8976-1' grown under three production systems.

*m*-Coumaric acid (mC) and *o*-Coumaric acid (oC); kaempferol was quantified using kaempferol-3-glucoside (K3G); flavonols were

5.2

53.5

4.7

33.5

65.2

100.0

 15.4b

 13.6b

20.6a 22.6a

81.2b

60.3b

4.4b 5.8a 6.2a

18.7a

206.3a

382.9a

17.4a

175.6ab

318.1ab

8.3b

144.2b

251.4b

2.7

5.1

15.8

0.8

5.9

30.1

50.3

 18.8a

 15.3b

19.6b 23.2ab

60.8b

48.8b

6.0b 7.5a 8.2a

28.9a

168.9a

22.2b

147.2a

11.1c

110.5b

211.3c

279.7b

330.7a

3.8

4.5

11.9

0.8

3.9

28.0

55.3

208 Phenolic Compounds - Natural Sources, Importance and Applications

 19.3a

 11.9b

18.9b 22.3b

52.4b

41.7b

4.2b 4.9b 5.8a

8.9a

144.6a

278.0a

7.2a

120.7ab

226.7ab

5.3a

97.8b

179.8b

**(254 nm)**

**Ellagic acid** 

**Total benzoic** 

**Total hydroxycinnamic** 

**Total kaempferol** 

**Total flavonols** 

**Total anthocyanins** 

**Total phenolics—**

**sum of 6 groups**

**(510 nm)**

**(350 nm)**

**(280 nm)**

**acids (280 nm)**

**acids (280 nm)**

Different lower-case letters in the same column indicate statistically significant differences between different treatments (*p* < 0.05).

**Table 6.** Early-, mid- and late-harvest phenolic composition (μg g−1 fresh frozen weight) of strawberry selection 'SJ8976-1' grown under three production systems.

These results are congruent with the findings of other researchers who indicated that significantly higher amounts of cyanidin-3-glycoside and pelargonidin-3-glycoside were assessed in strawberry fruits from hill plasticulture in comparison to MRS [19]. The consecutive experiment by Wang et al. also indicated that pelargonidin was the predominant anthocyanin in strawberry fruits [26]. Furthermore, the increased antioxidant capacity and phenolic compositions in berries may offer higher nutritional values to humankind [4, 30].
