I was wrong. I don't use TRIM.
If you change PREFIX from nop admin mode than NopCommerce TRIM each value automatically.
Open the feed template as plain file.
Example Google.xml and look for your prefix. Add space bar and save it.
<FeedAttribute>
<Id>1</Id>
<FeedCaption>Product Name</FeedCaption>
<FeedName>title</FeedName>
<FieldNameCode>name</FieldNameCode>
<Prefix>Test </Prefix>
<ConvertValues />
<CharsLimit>150</CharsLimit>
<Required>false</Required>
<IgnoreNullOrEmpty>false</IgnoreNullOrEmpty>
<UseCDATA>false</UseCDATA>
<ActionId>0</ActionId>
<AdvancedField>false</AdvancedField>
<RowSourceType>0</RowSourceType>
<AttributeControlType>0</AttributeControlType>
</FeedAttribute>