If, per profile, you're running 2016 I don't think you will be able to use TEXTJOIN, hence suggestion of UDF.

If you do have access to TEXTJOIN then another, slightly shorter, alternative would be:

Formula: copy to clipboard 
D4:

=TEXTJOIN(";",,INDEX(TEXT(TEXT(LEFT(TEXT(MID(SUBSTITUTE(SUBSTITUTE(SUBSTITUTE(B4&"@",": ",""),",","")," ","@"&REPT(" ",16)),ROW($1:$500),16),),15),"0;;;\0"),"[>"&$D$2&"]0;"""""),,0))

confirmed with Enter

where B4 holds your string, and D2 the min threshold (e.g. 50)